Low maintenance, gravity powered enhanced coagulation systems

Abstract

The subject of invention is an installation for enhanced coagulation, sedimentation with pre filtration on a sludge blanket and rapid sand filtration of the liquid industrial streams, in particular raw water or wastewater, comprising at least a first zone equipped with a hydraulic flocculator (1) for improved coagulation arranged upstream of the sedimentation device, a second zone equipped with a clarifier (2) for sedimentation with pre filtration from which is drawn the clarified water and a third zone equipped with filtration device(3). Also, the subject of the invention is a method of treating liquid industrial streams, in particular raw water or wastewater treatment in the installation of invention

Description

Low maintenance, gravity powered enhanced coagulation systems

[0001] The invention relates to technical field of enhanced coagulation and filtration. In particular, an application of this technology for the water treatment, wastewater treatment, pretreatment of raw water and other feedstocks of subsequent membrane purification, recovery of solids from the industrial streams, nutrient recovery from wastewater, tertiary treatment of effluent from biological wastewater treatment plants and for use in other related technical fields.

[0002] Based on literature [NPL: from 1 to 27] multiple water treatment technologies can be identified. These technologies can be broadly divided into three main categories – conventional flocculation / sedimentation / filtration systems, membrane filtration systems, and enhanced coagulation systems, relying on the same physical chemical phenomena as the first category, but using a wide range of techniques geared towards improving their performance. This division only includes non destructive separation methods based on physical phenomena, therefore excludes technologies relying on oxidation (UV treatment, ozonation, enhanced oxidation processes), sorption (ion exchange, activated carbon) or microbial treatment because of their reliance on chemically transforming contaminant, either by metabolizing it, chemically degrading or binding to the surface of a sorbent, rather than mechanically removing it from the water without any chemical conversion [NPL:1] and [NPL:2].

[0003] Conventional flocculation / sedimentation / filtration processes rely on destabilizing the colloid suspended in water, subsequent flocculation to form larger particles, followed by sedimentation by gravity or other external forces (centrifugal, electromagnetic), and by filtration of the clarified water. Common method of destabilizing colloid is by the addition of the salts of insoluble metals. In that process, coagulation occurs when the Al or Fe salts used as coagulant precipitate and neutralize the surface charge on the suspended colloid. Potential addition of polymers as flocculation aid can enhance floc formation in the subsequent flocculation (also known as “slow mixing”) process [NPL:3] and [NPL:4]. Other technologies include destabilizing colloidal suspension by the pH adjustment or by the use of natural polymers which enmesh suspended solids to form flocs. Due to the nature of these processes, they are not well suited for removing highly dispersed pollutants, such as low molecular weight natural organic matter (NOM), and solutes. Their effectiveness is further limited when dealing with contaminants showing low affinity to the formed flocs, such as PFAS and some of the ions. Removal of those fractions requires more advanced techniques, such as addition of sorbents or chemical treatment [NPL:5] and [NPL:6].

[0004] Despite their limitations, conventional treatment technologies are very well established and have been deployed as water treatment systems in various configurations for approximately 100 years. Regardless of their undeniable maturity, they are still facing some common technical problems. Large footprint of the plants results with significant space and tank volume requirement, increasing the capital expenditure (CAPEX). Additionally, conventional sedimentation tanks require periodic decommissioning for cleaning operations. Especially in the context of small municipal applications, this results with significant burden on the operation and maintenance (O&M) expenditure (OPEX). Finally, deterioration of natural water sources around the globe makes those solutions insufficient for delivering required effluent quality for some applications (such as human consumption or cooling). It is related to the above-mentioned inherent limitations of this technology, with respect to the scope of targeted pollutants.

[0005] Membrane processes typically use a series of physical barriers of different pore sizes, from a few micrometers for microfiltration all the way down to sub-nanometer pores for the reverse osmosis (RO) membranes, which are essentially considered non-porous. Membranes serve as barriers which allow specific fractions to permeate through, while stopping movement of some others. These methods are highly effective in removing wide range of contaminants but come with a couple of major drawbacks – membranes are prone to fouling, require costly cleaning operations using corrosive chemicals, their operation is energy intensive and results with discharges of significant amount of harmful waste.

[0006] Economic challenges of the membrane separation, especially visible in the operation and maintenance phase of the project, are related to the fact that it produces substantial volumes of wastewater from the cleaning cycles. In extreme cases, waste stream is higher in volume than the permeate (purified stream). It is especially problematic, as the waste stream produced in the backwashing process is either highly saline or has extreme pH values due to the use of cleaning chemicals. It is therefore costly to handle and has severe environmental impact [NPL:7]. Another problem with membrane processes, especially with the RO stage, is a requirement for high pressures necessary to push water through the non-porous membrane. Depending on the degree of the membrane fouling and the raw water quality, especially its ionic strength, RO requires from 60 to 80 bar pressure difference, consuming significant amount of energy [NPL:8].

[0007] Another class of solutions are enhanced flocculation systems. Those technologies rely on the chemical and physical principles of conventional process described previously, but incorporate various techniques to improve their efficiency. Prefiltration on the fluidized bed of sludge (so called “sludge blanket”) and plate settlers, used in the Superpulsator plants offered by SUEZ [NPL:9], are typical ways of enhancing coagulation process. Other example of technique enhancing the efficiency of coagulation is the use of various forms of ballast to improve settleability of the generated flocs. Technologies such as Actiflo offered by Veolia use ballast sand, while Sirofloc goes a step further and uses magnetite as a ballast, allowing for further improvement of the settling speed by exposing magnetite-rich flocs to the external magnetic field. Finally, some authors consider using elevated doses of coagulant as an enhancement to the flocculation process [NPL:10].

[0008] Another method for treating water by sedimentation, in which reagents are forced to circulate in a flow of untreated water, is known through the patent EP0330582B1. The auxiliary agents comprise coagulants as mineral salts (iron sulfate, aluminum sulfate, ferric chloride, etc.) which cause hydrolysis of the suspended materials, and flocculating agents (polymers of the "polyelectrolyte" type, etc.) which promote agglomeration and growth of the seeds thus formed. The aggregates, or flocs, thus formed then pass through one (or more) settling zones, at the upper part of which clarified water is recovered, and at the base of which sludge is removed and sometimes retreated after appropriate treatment.

[0009] The US7153423B2 patent disclosed an offshore wastewater treatment facility: wastewater treatment components (for preliminary treatment, primary treatment, secondary treatment, and / or advanced treatment); means for moving wastewater from a land-based site to the facility; means for removing treated wastewater from the facility; and means for removing sludge from the facility. A method of treating wastewater includes transporting wastewater from a site on land to a wastewater treatment facility located offshore in a body of water, and subjecting the wastewater to preliminary treatment, primary treatment, secondary treatment, and / or advanced treatment. The wastewater subjected to this treatment can be transported (e.g., by pipeline) to a facility located offshore (e.g., on a vessel moored in a body of water) for one or more of secondary treatment, disinfection, and advanced treatment. The resulting treated wastewater can be either discharged offshore or returned to the land for further processing or use. The resulting sludge can be transferred back to land for disposal or for further processing. The sludge might also be subjected to further treatment (e.g., digestion and / or dewatering) on the vessel before being returned to land.

[0010] The patent application JP2021186745A reveals a combined coagulation and membrane filtration system, with a coagulation treatment unit in which a coagulant is mixed with raw water and subject to slow mixing, and a membrane filtration unit that filters the pre-treated water obtained in the coagulation unit ona separation membrane. The coagulation treatment unit is provided with a rapid mix tank and a slow mix tank located after the rapid mix tank, and the hydraulic residence time of the tanks is provided.

[0011] The patent application CN102417247A describes a two-stage series coagulation process, which recycles part of the fresh sludge generated by the second stage coagulation to the first stage coagulation tank at a certain ratio. In the first stage coagulation, the operation mode of low coagulant dosage and sludge return is adopted to remove most of the pollutants. The returned fresh sludge contains flocs with a weak positive charge, and it is rich in hydroxyl active sites. After the return, the sludge can further exert its electrical neutralization or adsorption role to remove suspended particles from the water, thereby reducing the coagulant investment. At the same time, mature flocs contained in the returned sludge can be used as core particles to provide the necessary surface area for the formation of fresh flocs, thereby increasing the density of the final flocs and increasing the sedimentation rate of the first stage coagulated flocs. In the second stage coagulation, the operation mode of higher dosage of coagulant and no sludge return operation is used to further remove pollutants in the water and ensure the quality of the effluent. The second stage coagulation adopts the operation mode without sludge backflow. On one hand, it can provide fresh sludge for the first stage coagulation, instead of the "composite sludge" containing secondary use; on the other hand, the addition of coagulant can solve the problem of unstable operation caused by back mixing in first level coagulation.

[0012] The invention CN101244858A relates to a sewage coagulation method and a coagulation tubular reactor. The coagulation tubular reactor comprises a water inlet, a intensified coagulation system and a water outlet; the intensified coagulation systems is a series of connected intensified coagulation units, multiple coagulant inlets are arranged on bottom part and lateral side of each intensified coagulation system; the processing procedure is that: after the sewage enters into the intensified coagulation system via the water inlet, the chemical is mixed with sewage via the coagulant inlet and the mixture flows into the next sedimentation device via the water outlet to realize solid liquid separation.

[0013] The invention CN112794555A solves the problem of poor solid-liquid separation effect during single stage enhanced coagulation, through two stage coagulation under different pH environments. Presented invention proposes an aeration and pH-adjustment pool, set up before the first stage effulent enters the secondary coagulation, and the chemical equilibrium mechanism of carbonate and bicarbonate in the water is used to achieve pH adjustment through aeration. It saves the cost of adding alkaline agents to adjust the pH value and creates a suitable environment for the secondary coagulation to achieve good pollutant removal and solid-liquid separation. This method is suitable for various complex and difficult to treat industrial wastewaters, such as compost leachate, landfill leachate, thermally hydrolyzed sludge, fermented biogas slurry, sludge enhanced by cellular wall breaking (including oxidation, acid and alkali, mechanical, high temperature and high pressure, sludge thermal hydrolysis, ultrasonic and microwave, etc.), and so on. The method can also effectively remove various refractory pollutants and pollutants that inhibit biological activity, consequently creating good conditions for the subsequent biological treatment and discharge compliance.

[0014] The purpose of the present invention is to provide a high efficiency system for treatment of drinking water or other similar media that, compared to conventional setups of the same size, allows for greater throughputs, while decreasing the volume of produced waste, lowering energy demand, and limiting maintenance requirements. The low maintenance, self cleaning system described below has the potential to save costs associated with regular O&M decommissioning and cleaning of the tanks, decrease the volume of generated waste streams, as well as tackle one of the main societal problems related to the operation of the water treatment systems, by reducing the reliance on plant operators. The plant semi autonomy offered by the described system would offer a solution to the growing threat of the water industry’s aging and shrinking workforce.

[0015] The present invention is achieved through the following technical solutions.

[0016] Described solution tackles several technical problems associated with the operation of coagulation / sedimentation / filtration systems without experiencing drawbacks typically linked to the high-tech enhanced coagulation technologies.

[0017] At the first stage of the process – flocculation or “slow mixing” – a non-uniform mixing intensity in the flocculator tank results with suboptimal use of the tank volume. Mechanically mixed flocculators generate non-uniform velocity fields, which vary with the distance from the stirrer. As the distance from the stirrer increases, mixing intensity decreases, leading to insufficient collision rate between the particles, which consequently slows down the agglomeration rate. Close to the stirrer however, velocity gradient is much larger, which results with more intensive mixing. Shear stress caused by the fluid deformation in that zone leads to the floc breakdown and therefore works against the goal of the process. As a result, only a small fraction of the tank volume works in the optimal regime.

[0018] On top of that, conventional flocculators are built as continuously stirred tank reactors (CSTR). It is commonly known that CSTRs generally are low performance designs due to the reagent dilution. This issue applies to flocculation as well. Collisions between particles occur between the surfaces of the suspended solids. As particles agglomerate, less and less surface remains exposed for collisions, leading to the dilution effect by lowering the number of binding sited per unit volume of the liquid. These drawbacks result with relatively long flocculation times required by the US EPA standards for the CSTR flocculators – from 20 to 40 minutes [NPL:11]. Long flocculation times mean that this process requires large contact chambers and large agitators necessary to agitate the medium. Those are costly to build, complicated to maintain, consume significant amounts of energy and are prone to malfunctions.

[0019] The second stage of the process, sedimentation, can be conducted in horizontal or vertical clarifier basins. Those structures are simple and therefore extremely reliable, but their size is often very large – up to 12 hours of hydraulic residence time (HRT) for the horizontal flow clarifiers, according to the US EPA standards [NPL:11]. This results with substantial demand for space and associated high construction costs. Additionally, conventional sedimentation basins require decommissioning for cleaning, which is often a challenge for the O&M personnel.

[0020] Some of those drawbacks were overcome by enhanced sedimentation technologies, using systems of baffles, sludge blankets, sedimentation packets, ballast sand and recycling of the sludge components. Those devices offer high performance in a relatively small package (below 2 hours HRT) but are often very complex to build and operate. They require large valves, vacuum pumps, and elaborate automation, which makes them inherently prone to malfunction and their operation energy intensive and costly.

[0021] Rapid sand filtration is another mature technology which lacks optimization for better performance. Typical configuration of the sand filters involves vertical flow filters. Water flow through the filter is directed downwards in the filtration mode and reversed in the backwash cycle, after the filter becomes saturated with solids and requires cleaning. Backwash requires much higher flow rate (typically 5 to 6 times higher) than the filtration. As a result, cleaning of the filter can be done either by using a backwash water storage tank (which must be filled up before the backwash cycle) or by constructing multiple filters in a configuration where one can be backwashed using treated water from the remaining ones. Both solutions have their limitations. Storage tank offers limited capacity, inherently limiting the number of consecutive backwash cycles and leaving a narrow error margin for the operator’s mistakes. Multiple filters offer more flexibility, but they require substantial capital expenditure at the construction stage.

[0022] Finally, handling of the waste streams is a common problem for both conventional coagulation / sedimentation / filtration and enhanced coagulation technologies. Unlike sludge from the biological wastewater treatment, which was multiple technological applications, sludge from the water treatment clarifiers does not offer any beneficial use. At the same time, many legislatures consider it as a hazardous waste stream and therefore do not allow for unregulated disposal. Handling methods such as agricultural land disposal are controversial due to the general public’s perception, as well as a small likelihood of introducing harmful substances to the crops. As a result, landfill disposal is a common method of dealing with the clarifier sludge.

[0023] Proposed solution takes advantage of the flow mechanics and creative use of the flow channel geometry in order to optimize the use of space and decrease the need for maintenance operations. According to the invention, installation for enhanced coagulation, sedimentation with pre filtration on a sludge blanket and rapid sand filtration of the liquid industrial streams, in particular raw water or wastewater, comprises at least:

[0024] 1. A high efficiency hydraulic flocculator that leverages turbulent flow to promote floc formation while remaining free of moving parts, by ensuring a uniform distribution of minor pressure losses throughout the flocculator. Minor losses are dominant in turbulent flow and occur locally when the distances between the streamlines increase. By designing flocculator as a baffled flow channel in which the size of the baffles is selected to generate the same minor loss as the turn of the channel, and by spacing the flow obstructions (turns and baffles) apart within the range allowing minor loss to fully develop, it is possible to design a flocculator which ensures uniform velocity field throughout the entire reactor volume. Finally, this implies use of the plug flow reactor (PFR) design. PFRs take maximum advantage of the concentrated reagents, which further enhances performance. As a result, up to 20 times reduction of the flocculation chamber HRT can be achieved, compared with the conventional solutions, while eliminating all the moving parts.

[0025] 2. A self cleaning clarifier fitted with plate settlers and a sludge blanket system for efficient settling. Sludge blanket, a fluidized bed of precipitated solids recirculated within the clarifier until it reaches extremely high values of total suspended solids (TSS), serves as a process combining flocculation with filtration on the layer of suspended sludge. Small flocs leaving the flocculator collide with the sludge blanket circulating in the clarifier, thus being removed from water and incorporated in the filtration media. After the sludge blanket, ascending flow in the clarifier goes through the set of narrow spaced plate settlers. Sludge blanket process ensures very low turbidities of the clarified water, which decreases particulate loading on the plate settlers and allows for reduction of the distance between the plates. As a result, performance of the plates improves significantly compared with solutions designed for the use without the sludge blanket, driving the overall efficiency further up. Unlike current solutions, described clarifier uses a bottom geometry combined with a specialized diffusor for suspending the fluidized bed of sludge using the energy of the flow, without the need for vacuum pumps.

[0026] 3. A horizontal flow rapid sand filter, that decreases the hydraulic loading rate for a given flow and sand bed volume. Described design results in improved stability of the particles in the filter, while having the capability of performing backwash operations without the need for pumps. It is achieved by feeding water into the filtration chamber through the inlet tank with several pipe stubs, which elevate inlets to all the diffusors but the lowest one. When the backwash valve is open, hydraulic siphon is activated which results with a pressure drop in the filter tank. Due to the suction, water level in the inlet tank drops below the pipe stubs. Effectively, elevated inlets become exposed above the water surface, which prevents water access to those lines. Only the lowest line receives water, which changes the flow from horizontal to vertical upwards (from the lowest diffusor at the tank bottom to the backwash water drain in the top). Smaller cross section of the tank in the top view than in the side view, results with higher local flow velocities during the up flow operation, which fluidizes and cleans the filtration media. Closing the backwash valve deactivates the siphon, submerges previously exposed pipe stubs, and restores normal operation in the filtration mode. Use of inclined covers (“roofs”) creating void spaces in the filter bed instead of slotted pipes or other conventional diffusor designs decreases potential for fouling of the filter inlets and outlets due to scaling or other form of particle deposition. Area underneath the roofs is selected for the design flow rate and predicted filter medium to ensure that the medium will not be carried by the flow to the filter outlet tank.

[0027] 4. Continuous sludge treatment and recycling process. Majority of the sludge produced in the system comes from the clarifier. Upon reaching the design height, sludge blanket starts to pour over the weir into the secondary sedimentation chamber. Excessive sludge accumulated in the secondary clarifier chamber goes through the gravity compaction and is then drained to the continuous sludge dewatering and treatment system using Fenton like advanced oxidation process (AOP) to degrade contaminants and regenerate coagulant. Sludge pH is brought down in a CSTR tank, to the point when metal salts (typically iron, either introduced as ferric coagulant or naturally present in the sludge) dissolve increasing the catalyst concentration in the stream. At this point, mixture is rich in various catalysts for the Fenton like process (Fe2+ / 3+ ion system, other metals, natural organic matter, proteins, etc.). It is then mixed with hydrogen peroxide and directed to another PFR in which organic fraction is degraded. Hydrogen peroxide, exposed to the catalysts, decomposes into hydroxyl radicals which oxidize constituents of the sludge. Use of the PFR instead of the conventional CSTR for the AOP allows for lowering HRT from hours to minutes, contributing greatly to the reaction efficiency [NPL:22]. Depending on the goal of the process, oxidation can be done to the point of complete mineralization of the organics or only detoxifying and improving bioavailability of the contaminants. Post treatment mixture is rich in dissolved metal salts, undissolved solids present in the original treated stream, and free of toxic organics which were degraded by the oxidant. After separating the solids, liquid fraction can be recycled back to the flocculator for coagulant regeneration and enhancement of the microbial growth if microbiological treatment is of interest. Additionally, solids can be recycled back to the flocculator as well, for the ballasted flocculation. In the extreme case of low TSS in the treated stream, sludge can be recycled entirely without any processing and serve as a ballast. Adjustment of the proportion between the recycled treated sludge, wasted sludge, and recycled post treatment solids, as well as specific treatment conditions (e.g., oxidant concentration, pH), allow to control the impact of the sludge handling process on the overall treatment.

[0028] The invention also relates to a method of treating liquid industrial streams, in particular raw water or wastewater treatment in the installation of invention, the method comprises:a coagulation step, wherein a predefined stream of wastewater and coagulant is passed through the raw water inlet and coagulant injection point into hydraulic flocculator provided with static rapid mixer and with passive mixing baffles inside the pipe segment;a slow mixing said so formed mixture with horizontal flow through the channels, with an inlet at the top of the device and the outlet at the bottom, in order to induce the formation of large flocs;a clarification step, wherein a said mixture, substantially flocculated enters the clarifier through the inlet diffusor with nozzles positioned off center to allow for reversal of the water stream on the semi tubular geometry of the tank bottom, wherein water exiting from the nozzles resuspends the particles sliding down the inclined walls of the tank, thus generating a layer of fluidized sludge bed with a high density of suspended solids (TSS of 1000 mg / l or more);a preliminary filtration stage for the said flocculated water in a so called sludge blanket process is carried out at flow velocity of 1 mm / s (calculated for the overall footprint of the tank, disregarding the area of the sludge compaction chamber), wherein solids build up in the fluidized bed chamber until they reach the top of the weir separating it from the sludge compaction compartment which can be either removed in a batch mode, by simple opening of the valve, or in a continuous mode using a flow control valve;a polishing filtration step using the three chamber horizontal flow sand filter; wherein the clarified water enters the horizontal flow sand filter through the filter inlet tank feeding water through several pipe stubs, which elevate inlets to all the diffusors but the lowest one, wherein as contaminants accumulate in the filter bed, the pressure drop across the filter increases and the water level in the pre tank increases which causes the opening of the valve located on the backwash waste line causing a drop in the water level in both influent and effluent tanks, which prevents water from entering upper layers and allows for backwashing the entire tank without the risk of contaminating clear well with the backwash waste;finally, the water after passing through the media inside the filter during the filtration mode reaches a filtered water tank and can be used;and backwashing said filter, for the final disposal of said predefined quantity of collected solids.

[0029] Overall, described solution relies mainly on passive components, i.e. it does not require mechanical mixing and only includes a few moving parts (such as control valves and dosing pumps). Application of techniques geared towards improving performance allows for decreasing sizes of the tanks, which not only saves CAPEX, but also allows for more effective automatic control using simple feedback controllers. Additionally, the use of PFRs and other enhancements of the treatment train efficiency, as well as a careful hydraulic design, optimize the operation and brings down the HRTs, contributing to lower capital and operational costs. Finally, innovative use of the Fenton-like AOP opens path for the first industrial application of the clarifier sludge form the surface water coagulation process.

[0030] Proposed coagulation / flocculation process is highly effective due to the appropriate selection of the baffle geometry – dimensions of the small constrictions are selected so that at the design flow rate the minor pressure loss over the constriction is equal to the minor pressure loss over the 180 degrees bent in the flocculation channel. Spacing between the obstacles (constrictions and bends) is selected for each design based on the CFD analysis, to match the distance downstream at which the minor loss occurs. This design ensures uniform energy dissipation throughout the entire flocculator, and therefore allows for minimizing dead volume (where mixing is too slow for effective flocculation) and the high shear zones (where mixing is so fast that it breaks the flocs apart). By selecting appropriate energy dissipation rate, which is proportional to the velocity gradient in the flocculator and consequently to the mixing intensity, entire volume of the reactor can operate at the same design mixing rate.

[0031] Proposed clarifier uses the sludge blanket process, which combines features of flocculation and filtration. As a result, it can be run with smaller flocculators and offers greater performance than the conventional clarifiers. Additionally, high efficiency of the sludge blanket process decreases the TSS of water and enables the use of narrow spaced plate settlers. Finally, secondary sedimentation basin in the clarifier produces continuous stream of sludge which can be drained to waste or directed to further processing.

[0032] Described sand filter allows for depositing more solids in the given volume of the filter medium. By decreasing local flow velocities, shear stress on the solids deposited in the filter is minimized. Consequently, collected solids are more stable and less prone to being displaced from the filter bed. Innovative diffusors and drainage systems, using gravity to prevent filter medium from being washed out of the filter, ensure that the system will not clog due to scaling or solids deposition in the fittings.

[0033] Sludge treatment process decreases toxicity of the produced waste stream. It also allows for recycling spent coagulant for reuse or as a ballast material to enhance sedimentation.

[0034] Additionally, entire solution is more reliable due to the limited use of the moving parts. Mechanical components are inherently prone to wear and tear, which results with the need for replacement. As it does not rely on mechanical mixing, proposed technology has low electricity demand.

[0035] Finally, small size of the tanks allows for improved automatic control of the system compared with available alternatives. The decrease of HRT between the coagulant injection port and the clarifier inlet from more 8 to 12 hours down to less than an hour allows for managing coagulant dosing using a simple feedback based on the clarified water quality. Instead of using indirect, less reliable methods, or depending on the constant supervision by the plant operator, a simple PID controller can achieve stable operation of the plant.

[0036] In the method according to invention, the sludge oxidation process can be run as a coagulant regeneration process, to reduce volume of the sludge and reuse coagulant. Depending on the redox conditions in the reactor, it can be operated as a sludge detoxifying process, to completely mineralize organic matter present in the sludge, or as a source of bioavailable dissolved organic matter, to enhance microbial growth in the sludge blanket or in the filter. Sludge recycling stream can be also run without altering the sludge composition, wherein the compacted sludge from the clarifier serves as a source of ballasting agent which enhances performance of the process, especially in the conditions of low raw water turbidity (<1 NTU).

[0037] presents a diagram of spatial arrangement of water treatment station elements

[0038] presents a pipe flocculator

[0039] presents a clarifier with a sludge blanket system inside (top) and outside geometry (bottom)

[0040] presents a diagram of the construction of the clarifier in the side view (construction of the diffuser)

[0041] presents a diagram of the construction of the filter

[0042] presents a diagram of entire installation in the filtration mode

[0043] presents an entire installation in the backwash mode – hydraulic siphon after opening the control valve on the backwash drain line generates suction which leads to lowering the water level in the inlet and outlet tanks, as well as fluidizes the filtration mediaExamples

[0044] Example 1: High efficiency hydraulic flocculatorand

[0045] The high efficiency hydraulic flocculator (1) is a designed in the form of straight pipe segments (9) connected by return elbows, equipped with in-line mixers in the form of baffles (8) placed inside the straight pipe sections and with a passive rapid mix (7) for dispersing coagulant. It is designed to operate at Reynolds numbers at the order for magnitude 10^4, to ensure that the minor losses are dominant mechanism of energy dissipation in the system. Passive mixers in the form of baffles (5) are designed and spaced to ensure optimal generation of suspension of larger particles, occurring at the flow velocity gradient of approximately 180 1 / s. By maintaining a homogeneous flow velocity field, the installation according to the invention ensures effective collisions between the suspended particles, without generating excessive shear stresses that could lead to tearing of the resulting agglomerates. The design of the flocculator (1) guarantees sufficient slow mixing at the HRT of 2 minutes and optimal conditions for the formation of large flocs, without the need for mechanical mixing. This minimizes service requirements and reduces power consumption.

[0046] Referring to, a pipe flocculator (1) according to the invention is sealed, fitted with raw water inlet (4), connected with raw water flow control valve (5), coagulant injection point (6), passive rapid mix (7), straight pipe segments (9) characterized by a rounded cross section with internally located pipe baffles (8) and a flocculated water outlet (11) to allow for emptying the tank and, if needed, for draining the coarse sediment fraction building up in the tank during the high turbidity events. The components of hydraulic flocculator (1) are fixed on a support frame (10) advantageously with wheels. Inside each pipe, baffles (8) are evenly distributed on the threaded rod ended with a mixing disk for fixation. On a rod with a length of 2000 mm, 5 pipe baffles (8) are placed, with the distance between the mixing disk for fixation and the first pipe baffle (8) being 5 mm less than the distances between subsequent pipe baffles (8). Horizontal flow through the pipe segment (9) with internal baffles (8), with an inlet at the top of the tank and the outlet at the bottom, allows for moving the sediment down towards the drain and therefore prevents buildups within the tank.

[0047] Example 2: Self cleaning clarifier fitted with a pre filtration on the fluidized sludge bed and a sludge compaction compartmentand

[0048] Referring to, a self cleaning clarifier (2) fitted with a pre-filtration on the fluidized sludge bed and a sludge compaction compartment according to the invention is fitted with suspended settling plates (12) fixed to support frame (13) which encloses on four sides the main tank of the clarifier (14) with sludge drain (15) situated below and clarified water manifold (16) situated above the main tank of the clarifier (14) with internal located plate settlers (17). On the bottom of main tank of the clarifier (14) opposite to sludge drain (15) the inlet diffusor (18), service drain (19) and pressure washer attachment (20) are located. In the middle of clarifier the secondary clarification chamber (21), sludge weir (22), sludge blanket chamber (23) and inlet diffusor nozzles (24) are situated.

[0049] Water enters the clarifier through the inlet manifold (16) with nozzles positioned off center, to allow for the water stream reversal on the semi tubular geometry of the tank bottom. Water exiting from the nozzles resuspends the particles sliding down the inclined walls of the main tank of the clarifier (14), thus generating a layer of fluidized sludge bed with a high density of suspended solids. Fluidized bed serves as a preliminary filtration stage for the flocculated water in a so-called sludge blanket process, and the particles it captures become incorporated into the filtration bed, therefore increasing its volume. Up flow velocity of 1 mm / s (calculated for the overall footprint of the tank, disregarding the area of the sludge compaction chamber) is used.

[0050] After the initial start up, as clarifier approaches the steady state operation, solids build up in the fluidized bed chamber until they reach the top of the weir separating it from the sludge compaction compartment. At that point, sludge used in the fluidized bed filtration is compacted under its own weight and can subsequently be removed from the system through the simple opening of a valve. This, combined with the inclined walls of the secondary clarification chamber (21), allows for de facto self-cleaning operation of the clarifier, without the need for maintenance stopovers for cleaning. Compacted sludge can be either removed in a batch mode, by simple opening of the valve, or in a continuous mode using a flow control valve. Sludge weir is inclined at 75 deg and the area of the secondary clarification chamber (21) is equal to 20% of the total clarifier footprint.

[0051] Clarifier is also fitted with internal located plate settlers (17), in order to further optimize performance and remove particles not captured by the process carried up from the fluidized bed compartment by the up flow water current. Plates are inclined at 60deg and spaced 25 mm apart. Length of the internal located palate settlers (17) is selected as maximum dimension fitting in the tank, which allows for 10 cm clearance between the sludge weir and plates, as well as 10 cm clearance between the clarified water manifold and the plates.

[0052] Example 3: Horizontal flow sand filterandto

[0053] Thetovisualize the filter section.

[0054] A support frame (33) consisting of three columns include centrally located main filter tank (31) with attached both sided filtered water tank (30) known also as a “clear well” on one side, and filter inlet tank (32) on the other side. On the top of main filter tank (31) filter media port (25) is attached and on its back wall backwash valve (26) is located. On the back side of main filter tank (31), approximately at the height of the bottom edge of filtered water tank (30) and filter inlet tank (32) and below, the filtered water drains (27), inlet diffusors (28) and backwash diffusor (29) are fixed. Whereas, on the front of main filter tank (31) the filtration media drain (34) and pressure washer connection (35) are attached.

[0055] Water enters the filter through the filter inlet tank (32), fitted with tubes extending to different heights. The line feeding the lowest layer of the filter has the largest diameter and ends at the level of the tank bottom, while all the remaining lines end higher. Bottom line has to be designed to minimize pressure loss at the flow rate equal to the design capacity of the entire system – for the case of 3 m^3 / h, flexible suction hose ND50 is used. Remaining lines are ND50 for simplicity, but they can be narrower if needed, of nominal diameters allowing to handle fraction of the total flow which goes to given manifold. All the lines are running down to the level of the main filter tank (31) bottom, in order to ensure hydraulic seal during the backwash process, and are then run up to their corresponding layers of the filter media.

[0056] Water is fed to each layer of the filter through the tubes connected underneath the inclined cover creating a particle free volume, which de facto becomes an inlet manifold for its’ corresponding layer. After passing through the media, water reaches a similar pseudo-manifold and is drained. The area underneath each cover is crucial design parameter for the water drain system, it has to be large enough to ensure that the water flow during the normal filter operation does not cause lifting of the filter media and subsequent carrying of the particles down to the effluent tank and to the clear well. For the proposed filter medium, anthracite with particle size of 0.6 to 1.5 mm, local flow velocity should be kept below 10 m / h.

[0057] At the moment when the filter head loss reaches a maximum desired value determined at the design stage, entire filter bed (all the layers) are backwashed at once, by opening a valve located on the backwash waste line (running from the top of the filter). After opening the valve, created siphon suspends the filtration bed, at the same time causing a drop in the water level in both influent and effluent tanks. This fact, combined with different heights of the tubes, effectively prevents water from entering upper layers, only the lowest part of the filter receives water, which allows for backwashing the entire tank without the risk of contaminating clear well with the backwash waste. Up flow velocity of 35 m / h allows for 25% expansion of the filtration media, which has to be corrected for the safety factor of 50%, for 37.5% maximum expansion, to accommodate for temperature changes or operation at higher flow rates.

[0058] Example 4: Plug flow reactor for the continuous sludge treatment and particle regeneration

[0059] Sludge from the compaction compartment of the clarifier (2) is continuously drained and the sludge can be fed to the plug flow reactor (PFR) using Fenton’s process for degrading the organic phase of sludge. Catalyst for the Fenton’s process can come either from the solids naturally present in the water or from artificial source, such as the ferric coagulant which might be used for the flocculation process. Lowering the pH prior to the hydrogen peroxide dosing will allow to dissolve the coagulant precipitate, thus facilitating solids separation and generating metal ions which will become a homogeneous catalyst for Fenton’s process. Reaction mixture will be then mixed with a hydrogen peroxide solution and fed to a PFR for the oxidative treatment. Depending on the chosen strategy of running the process, different characteristics of the reaction mixture can be achieved. Reagents after the treatment will be either free of organic contaminants or will contain easily biodegradable organics ready for microbiological treatment. In both cases, it will be rich in metal ions which can serve as a coagulant. Consequently, after separation of the solids still present in suspension, it can be recycled to the beginning of the treatment process to decrease demand for a new coagulant and potentially serve as a source of bioavailable carbon to facilitate achieving biologically active sludge blanket and biologically active sand filter. If oxidative process is used, solids separated from the reaction mixture will be the only waste stream discarded from the process.

[0060] Example 5: Process in the normal operation mode

[0061] This process is shown in the, which also indicates approximate water levels, spaces where sediment accumulates, and zone occupied by the filtration bed. In the filter backwash mode, hydraulic siphon after opening the control valve on the backwash drain line generates suction which leads to lowering the water level in the inlet and outlet tanks, as well as fluidizes the filtration media. Fluidization allows for mechanical removal of accumulated solids from the sand bed, consequently regenerating the filter.

[0062] 1 flocculator

[0063] 2 clarifier

[0064] 3 filter

[0065] 4 raw water inlet

[0066] 5 raw water control valve

[0067] 6 coagulant injection port

[0068] 7 static mixer

[0069] 8 baffles (inside the pipe)

[0070] 9 pipe segment

[0071] 10 support frame

[0072] 11 flocculated water outlet / post coagulation water connection

[0073] 12 plate settlers mount

[0074] 13 support frame

[0075] 14 body (main tank) of the clarifier

[0076] 15 sludge drain

[0077] 16 clarified water manifold

[0078] 17 plate settler package (inside the clarifier)

[0079] 18 inlet manifold with nozzles positioned off-center

[0080] 19 service drain

[0081] 20 connection to pressure washer

[0082] 21 secondary clarifier chamber

[0083] 22 sludge weir

[0084] 23 suspended sludge chamber

[0085] 24 inlet diffuser nozzles.

[0086] 25 filter media port

[0087] 26 backwash valve

[0088] 27 filter drainage assembly

[0089] 28 diffuser assembly

[0090] 29 backwash diffuser

[0091] 30 post filtration tank for filtered water

[0092] 31 main tank

[0093] 32 pre tank

[0094] 33 support frame

[0095] 34 filter media drain

[0096] 35 pressure washer connectionNon Patent Literature

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Claims

An installation for enhanced coagulation, sedimentation with pre filtration on a sludge blanket and rapid sand filtration of the liquid industrial streams, in particular raw water or wastewater, comprising at least: a first zone equipped with a hydraulic flocculator (1) for improved coagulation, arranged upstream of the sedimentation device, a second zone equipped with a clarifier (2) for sedimentation with pre filtration from which is drawn the clarified water and a third zone equipped with filtration device(3), characterized in that:the hydraulic flocculator (1) is a PFR type flocculator designed in the form conduit having straight channel sections of circular or rectangular shape and connected by 180 degrees turns, the flocculator (1) is equipped with a raw water inlet (4), a coagulant injection point (6), a flocculated water outlet (11) and a static rapid mixer (7) placed inside the first straight segment of the conduit and with passive mixing inserts in the form of baffles (9) inside the subsequent sections (8), wherein the flocculator (1) has flow velocity gradient of 180 1 / s at the HRT of 2 minutes; and / orthe clarifier (2) is in the form of self-cleaning device fitted with plate settlers (12,14, 17), a sludge blanket system (15, 21, 22, 23), a clarified water manifold (16), an inlet diffusor (18) with nozzles positioned off center, further the clarifier (2) is equipped with a secondary sludge compaction zone (21) placed within the body of the clarifier, designed as a variation of the Imhoff cone and separated from the sludge blanket system (15, 21, 22, 23) with a sludge weir (22), wherein said plate settlers (12, 14, 17) are inclined at 60 deg and spaced less than 50 mm apart and sludge weir (22) is vertical at the side of the sludge blanket and inclined at 75 deg, so that the sludge blanket in the form of fluidized bed of precipitated solids is recirculated within the clarifier until it reaches extremely high values of total suspended solids and self cleans by passing into the secondary clarification chamber where it can freely slide down the walls of the Imhoff cone like structure (21); and / orthe filtration device (3) is in the form of a gravity powered horizontal flow sand filter (3) with vertical flow during the backwash cycle, comprising a filter inlet tank (32), main filter tank (31) with diffuser system (27, 28, 29), and with filtered water tank (30), wherein the water or other clarifier effluent flow with the local velocity of up to 10 m / h during the filtration cycle and up to 50 m / h during the backwash cycle.The installation according to claim 1, characterized in that the flocculator (1) is a pipe or rectangular channel flocculator to operate at Reynolds numbers at the order of magnitude 10^4.The installation according to claim 1, characterized in that the flocculator (1) is equipped with passive mixing baffles (9) in the form of disk cutouts or rectangular shapes locally restricting the flow of the flocculated media to generate minor head losses.The installation according to claim 3, characterized in that the passive mixing baffles (9) are sized based on the CFD simulations, preferably the maximum distance between the baffles (9) is between 4 and 9 hydraulic diameters of the constricted channel.The installation according to claim 1, characterized in that the clarifier (2) is a clarifier with a sludge blanket system (15, 21, 22, 23) formed upon flow mechanics via the resuspension of the sliding sediment by the jet of water with no additional moving parts.The installation according to claim 1, characterized in that the clarifier (2) is fitted with the narrow spaced plate settlers (12, 14, 17) or honeycomb sedimentation package, with conduits spaced 50 mm or less apart, with a length of the conduit selected as maximum dimension fitting in the tank, which allows for 10 cm clearance between the sludge weir and plates, as well as 10 cm clearance between the clarified water manifold and the plates.The installation according to claims 5 6, characterized in that the clarifier (2) tank bottom is inclined at an angle between 50 and 70 degrees, to ensure flow of the sludge towards the tank bottom, wherein the lowest point on the clarifier tank bottom has a shape of a half pipe of approximately 75 mm diameter, which serves for reversing the stream of water entering the tank.The installation according to claims 5-7, characterized in that the clarifier (2) inlet diffusor (18) is in the form of a straight pipe with a row of nozzles (24) pointing downwards, positioned approximately 35 mm to the side of the clarifier (2) center line, to direct the stream of water from the nozzles (24) along the half pipe and reverse it forming a uniform flat jet of water directed upwards to resuspend sediment sliding down the clarifier bottom.The installation according to claim 8, characterized in that the nozzles (24) geometry is in the form of a tube, in which the length of the nozzle is about 5 times larger than the diameter of the nozzle, wherein the diameters of the nozzles are selected so that the head loss on the nozzle is about 10 times higher than the kinematic pressure of the water at the beginning of the manifold, when Δp >> 1 / 2*ρ*v^2 where Δp is a head loss on a nozzle, ρ is a density of the treated liquid and v is the flow velocity at the beginning of the manifold.The installation according to claim 1, characterized in that the horizontal flow sand filter (3) is a three-chamber rapid sand filter, where main filter tank (31) bottom and inclined covers are tilted not less than 45 degrees, to ensure no deposition of stagnant filtration bed during the backwash process, wherein filter medium is preferably an anthracite with particle size of 0,6 to 1,5 mm.The installation according to claim 10, characterized in that the height of the bottom of the filter inlet (26) and the outlet of the backwash diffusor (29) are selected so that the water column pressure between them will not exceed the backwash head loss.The installation according to claim 10, characterized in that the drain of the filter outlet (34) is elevated to submerge elevated pipe stubs in the filter outlet.The installation according to claim 10, characterized in that the lowest points of the connections between the filter tanks are run not higher than 0.25 of the distance between the backwash drain outlet (34) and the elevated pipe stubs in the filter inlet (28).The installation according to claim 10, characterized in that the backwash diffusor (29) used to feed water is located so that it will feed water to the lowest part of the inclined bottom of the filtration tank (31), in order to ensure that the filter media slides down towards the manifold and is there resuspended during the backwash process.The installation according to claim 10, characterized in that the distance between the diffusors (27, 28, 29) and the drainage (34), i.e. depth of the filtration bed in the horizontal flow, does not cause pressure loss higher than 50 mBar, wherein the distance should be around 30 cm, but it can be modified for coarser or finer filtration media.The installation according to claim 10, characterized in that the height of the elevated pipe stubs in the filter inlet tank (32) and the drain of the filter outlet tank are selected so that it will not exceed height of the water column equivalent to the clean bed head lossThe installation according to claim 10, characterized in that the height of the elevated pipe stubs in the filter (31) inlet and the outlet of the backwash pipe are selected so that the water column pressure between them will exceed the backwash head loss.The installation according to claim 10, characterized in that the filtration velocity is calculated by dividing the design flow rate by the total area underneath the inclined covers and modified for the design flowrate by manipulating the filter tank dimensions, wherein is adjusted for the filtration media to ensure clean bed head loss below 100 mBar and no fluidization of the filtration media underneath the inclined covers, therefore ensuring that the filtration media does not leave the filter during the regular filtration.The installation according to claim 10, characterized in that the backwash velocity is calculated by dividing the design flow rate by the total top view area of the clarifier tank. It is adjusted by manipulating the filter tank dimensions and kept in the range which allows fluidization and expansion of the filter media for the backwash cycle, while keeping the head loss during the backwash process below 300 mBar.The installation according to any of claims 1-19 characterized in that further comprises peripheral devices and a controller with software to control the coagulant dosing using a feedback signal from the clarified water turbidity measurement, a proprietary model for predictive control logic or a combination of the two in the form of a feedback / feedforward fuzzy control logic.The installation according to any of the preceding claims, characterized in that further comprise a plug flow reactor (PFR) using Fenton like oxidation process (AOP) for degrading the organic phase of sludge from the compaction compartment of the clarifier (2).A method of treating liquid industrial streams, in particular raw water or wastewater treatment in the installation of any one of claims 1-21 characterized in that the method comprises following steps:a predefined stream of wastewater and coagulant is passed through the raw water inlet (4) and coagulant injection point (6) into hydraulic flocculator (1) provided with static rapid mixer (7) and with passive mixing baffles (9) inside the pipe segment (8);slow mixing said the so formed mixture with horizontal flow through the channels, with an inlet at the top (4) of the device and the outlet (11) at the bottom, in order to induce the formation of large flocs;sending a said mixture, substantially flocculated to clarifier (2) through the inlet diffusor with nozzles (18) positioned off center to allow for the wastewater stream reversal on the semi tubular geometry of the tank bottom, wherein water exiting from the nozzles resuspends the particles sliding down the inclined walls of the tank, thus generating a layer of fluidized sludge bed with a high density of suspended solids (TSS of 1000 mg / l or more);preliminary filtration stage for the said flocculated water in a so called sludge blanket process is carried out at flow velocity of 1 mm / s (calculated for the overall footprint of the tank, disregarding the area of the sludge compaction chamber), wherein solids build up in the fluidized bed chamber until they reach the top of the weir separating it from the sludge compaction compartment which can be either removed in a batch mode, by simple opening of the valve, or in a continuous mode using a flow control valve;polishing clarification step using the narrow-spaced plate settlers (12, 14, 17) or honeycomb sedimentation package;sending the clarified water into the horizontal flow sand filter (3) through the filter inlet tank (32) feeding water through several pipe stubs (27,28), which elevate inlets to all the diffusors but the lowest one (29), wherein as contaminants accumulate in the filter bed (31), the pressure drop across the filter increases and the water level in the pre tank (32) increases which causes the opening of the valve located on the backwash waste (35) line causing a drop in the water level in both influent (32) and effluent (30) tanks, which prevents water from entering upper layers and allows for backwashing the entire tank without the risk of contaminating clear well with the backwash waste;water after passing through the media inside the filter during the filtration mode reaches a filtered water tank (30) and can be used;backwashing said filter (3), for the final disposal of said predefined quantity of collected solids.The method according to claim 22, characterized in that in the step a) as coagulant is used iron or aluminum salt, preferably iron salt.The method according to claim 22, characterized in that the backwash process in the step f) is run for 7 minutes or until the turbidity of the backwash stream is equal to the turbidity of the settled water used for backwashing the filter media.The method according to claims 22 24, characterized in that the sludge formed in steps from a) to e) is directed to secondary clarifier chamber (21) for subsequent compaction and further compacted sludge is disposed of or directly transported to the continuous sludge dewatering and treatment system using Fenton like AOP.The method according to claim 25, characterized in that the sludge is oxidized at steps a) to e) or compaction step and the resulted reaction mixture can be recycled back into the flocculator (1), depending on the goal of the process.

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