Methods and related apparatus for processing biosolids

Abstract

Methods of biosolids processing disclosed herein include the step of distributing biosolids in an input state onto an outer circumference of a thermal floor disposed within a greenhouse, the thermal floor adapted to transfer heat to the biosolids and thereby transform the biosolids from the input state into a first processed state by heating the biosolids while spirally transferring the biosolids from the outer circumference to an inner circumference of the thermal floor. The method includes the step of distributing the biosolids in the first processed state onto a conveyance and then further heating the biosolids and thereby transforming the biosolids from the first processed state into a second processed state. Apparatus that functions to implement the methods are also disclosed.

Description

METHODS AND RELATED APPARATUS FOR PROCESSING BIOSOLIDSBACKGROUND OF THE INVENTIONField

[0001] The present application relates to processing of biosolids produced by wastewater treatment processes, in particular to methods and related apparatus that produce biosolids meeting certain standards.Background

[0002] Wastewater treatment plants produce and must dispose of residual solids collected as part of the wastewater treatment process (known as biosolids or sludge). Many wastewater treatment plants haul biosolids by truck to be land applied or landfilled, and generally pay for both the hauling and the disposal by weight of the biosolids.

[0003] Mechanical dewatering processes may typically produce biosolids having total solids (TS) generally in a range of from about 15% to about 25%. Clearly, the majority of the biosolids weight is due to water in this range of TS. Transporting this weight of this water adds significantly to the cost of disposal of the biosolids. Technologies that can further remove water from biosolids can significantly reduce disposal costs as well as reduce environmental impacts arising from transport of the biosolids.

[0004] In addition, treatment of biosolids to certain standards may allow for certain uses of the biosolids alternative to landfill disposal. For example, the United States Environmental Protection Agency (USEPA) defines the microbiological loading that is acceptable for unrestricted use of biosolids following treatment. As defined by the USEPA, there are several classes of produced biosolids ranging in quality and acceptable use. For example, Class A biosolids may be used as a soil amendment or fuel. Class A biosolids require a greater level of treatment to reduce the microbial population than Class B biosolids. However, Class A biosolids have more uses than Class B biosolids. This includes marketing the product as a soil amendment. Biosolids treated to Class A standard are defined by 40 Code of Federal Regulations (CFR) Part 503, Standards for the Use of Disposal of Sewage Sludge. Biosolids meeting Class Arequirement may have utility and corresponding economic value that may provide a revenue stream, not just a disposal cost.

[0005] Accordingly, there is a need for improved methods and related apparatus for treating biosolids.BRIEF SUMMARY OF THE INVENTION

[0006] These and other needs and disadvantages may be overcome by the methods and apparatus disclosed herein. Additional improvements and advantages may be recognized by those of ordinary skill in the art upon study of the present disclosure.

[0007] In various aspects, the methods include the step of distributing biosolids in an input state onto an outer circumference of a thermal floor of circular shape disposed within a greenhouse, the thermal floor adapted to transfer heat to the biosolids from a working fluid being communicated within the thermal floor, and the step of transforming the biosolids from the input state into a first processed state by heating the biosolids to a first temperature Ti for first detention time Di within the greenhouse while transferring the biosolids from the outer circumference of the thermal floor to an inner circumference of the thermal floor, in various aspects. The methods include the step of communicating the biosolids in the first processed state from the thermal floor onto a conveyance first end of a conveyance, in various aspects. The methods include the step of heating the biosolids to a second temperature T2 for second detention time D2 using a working fluid cooperating with the conveyance while conveying by the conveyance the biosolids from the conveyance first end to a conveyance second end thereby transforming the biosolids from the first processed state into a second processed state, the conveyance adapted to transfer heat from the working fluid to the biosolids while conveying the biosolids.

[0008] In various aspects, the biosolids processing apparatus includes a thermal floor disposed within a greenhouse with the thermal floor being circular and defining an outer circumference and an inner circumference. The thermal floor is adapted to transfer heat to the biosolids from a working fluid communicated through the thermal floor to heat the biosolids to a first temperature Ti for a first detention time Di in order to transform the biosolids from an input state proximate the outer circumference into a first processed state proximate the inner circumference, in variousaspects. The biosolids processing apparatus includes a biosolids handler that cooperates with the thermal floor to transfer the biosolids from the outer circumference to the inner circumference, in various aspects. The biosolids processing apparatus includes a conveyance defining a conveyance first end and a conveyance second end, and the conveyance is adapted to receive biosolids communicated from the inner circumference of the thermal floor by a conveyance first end of the conveyance, in various aspects. The conveyance is adapted to transfer heat from the working fluid to biosolids received by the conveyance in order to heat the biosolids to a second temperature T2 for second detention time D2 as the biosolids are being conveyed by the conveyance from the conveyance first end to a conveyance second end in order to transform the biosolids from the first processed state into a second processed state, in various aspects.

[0009] Methods and apparatus of biosolids processing disclosed herein may be configured in a two-stage process, in various aspects. The first stage, the second stage, or both the first stage and the second stage may be operated as either a batch or a continuous flow process, in various aspects. The biosolids in the second processed state meet a total solids standard of at least about 75%, in certain aspects. The biosolids in the second processed state, in various aspects, meet a microbial population standard selected from i) fecal coliform is belowl,000 MPN / g of dry solids; ii) Salmonella is measured at less than 3 MPN / 4g of dry solids; iii) less than 2,000,000 MPN / g of total solids (dry weight basis); or iv) less than 2,000,000 Colony Forming Units (CFU) per gram of total solids (dry weight basis). The greenhouse may be configured as a dome comprised of transparent material.

[0010] This summary is presented to provide a basic understanding of some aspects of the apparatus and methods disclosed herein as a prelude to the detailed description that follows below. Accordingly, this summary is not intended to identify key elements of the apparatus and methods disclosed herein or to delineate the scope thereof.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 illustrates by schematic diagram an exemplary biosolids processing apparatus including material flows through the exemplary biosolids drying apparatus;

[0012] Fig. 2 illustrates by cut-away elevation view portions of the exemplary biosolids processing apparatus of Fig. 1;

[0013] Fig. 3 illustrates by cut-away plan view portions of the exemplary biosolids processing apparatus of Fig. 1;

[0014] Fig. 4 illustrates by perspective view portions of the exemplary biosolids processing apparatus of Fig. 1; and,

[0015] Fig. 5 illustrates by process flow chart an exemplary process of drying biosolids as may be implemented using the exemplary biosolids processing apparatus of Fig. 1.

[0016] The Figures are exemplary only, and the implementations illustrated therein are selected to facilitate explanation. The number, position, relationship and dimensions of the elements shown in the Figures to form the various implementations described herein, as well as dimensions and dimensional proportions to conform to specific force, weight, strength, flow and similar requirements are explained herein or are understandable to a person of ordinary skill in the art upon study of this disclosure. Where used in the various Figures, the same numerals designate the same or similar elements. Furthermore, when the terms "top," "bottom," "right," "left," "forward," "rear," "first," "second," "inside," "outside," and similar terms are used, the terms should be understood in reference to the orientation of the implementations shown in the drawings and are utilized to facilitate description thereof. Use herein of relative terms such as generally, about, approximately, essentially, may be indicative of engineering, manufacturing, or scientific tolerances such as ±0.1%, ±1%, ±2.5%, ±5%, or other such tolerances, as would be recognized by those of ordinary skill in the art upon study of this disclosure.DETAILED DESCRIPTION OE THE INVENTION

[0017] Methods for biosolids processing and related biosolids processing apparatuses are disclosed herein. In various aspects, the methods are implemented using a two-stage process wherein a greenhouse that is heated comprises a first stage and a conveyance that is heated comprises a second stage of the two-stage process, with the first stage (e.g., the greenhouse) and the second stage (e.g., the conveyance) generally being configured as continuous plug flow processes. The methods and related biosolids processing apparatus may be sized and operated to output biosolids from the second stage in a second processed state meeting a standard, in various aspects. For example, the standard for biosolids in the second processed state may be given as water content of the biosolids so that total solids (TS) of the biosolids output from the second stage is equal to or exceeds a TS standard. Note that TS is given in percent by weight herein unless otherwise indicated. As another example, the standard for biosolids in the second processed state may meet a microbial population standard such as given in the USEPA Class A standard. Biosolids output from the first stage in first processed state may also meet a TS standard or microbial population standard, such as given in the USEPA Class B standard, in various aspects. In certain aspects, the process may comprise only a single stage comprising the greenhouse with the conveyance being configured only to convey the biosolids from the greenhouse without further treatment. While the first stage and the second stage are described herein as continuous flow processes, it should be recognized that the first stage may be operated as a batch process, the second stage may be operated as a batch process, or both the first stage and the second stage may be operated as batch processes, in various other aspects.

[0018] In various aspects, the methods include continuously distributing biosolids in an input state onto an outer circumference of a thermal floor having a circular shape and disposed within the greenhouse, and heating the biosolids by heating the thermal floor using a working fluid communicated within the thermal floor while transferring the biosolids from the outer circumference of the thermal floor to an inner circumference of the thermal floor thereby transforming the biosolids from the input state at the outer circumference to a first processed state at the inner circumference. In various aspects, the methods include collecting biosolids in the first processed state from the inner circumference onto a conveyance as output from the first stage, heating the biosolids by heating the conveyance using the working fluid as the biosolids are conveyed by the conveyance from a conveyance first end of the conveyance to a conveyancesecond end of the conveyance thereby transforming the biosolids from the first processed state at the conveyance first end to a second processed state at the conveyance second end. In various aspects, the methods include outputting biosolids in the second processed state from the conveyance second end of the conveyance. In various aspects, the methods include heating the working fluid using solar energy collected by a solar collector.

[0019] According to the USEPA as set forth in 40 CFR 503.32, the Class A standard is met when the percent solids of the sewage sludge is seventy-five percent or higher for digested sludge and ninety percent or higher for non-digested sludge, the temperature of the sewage sludge shall be 50 degrees Celsius or higher; the time period shall be 20 minutes or longer; and the temperature and time period shall be determined using equation (1) below, except when small particles of sewage sludge are heated by either warmed gases or an immiscible liquid,where detention time D = time in days and temperature T= temperature in degrees Celsius. Note that the 40 CFR 503.32 standard requires T > 50 °C and D > 20min / 1440 min / day = 0.0139 day. According to the Class A standard, the water content is reduced to TS of at least 75% for digested sludge and 90% for non-digested sludge. Testing must show that either fecal coliform is below 1,000 Most Probable Number (MPN) per gram of dry solids, or Salmonella is measured at less than 3 MPN / 4g of dry solids. Pathogens should be below detectable limits 24 hours after treatment or at the point of application. Class A should not exceed limits for As, Cd, Cr, Co, Pb, Hg, Mo, Ni, Se, Zn. At least 38% reduction in volatile solids should be observed.

[0020] According to the USEPA as set forth in 40 CFR 503.32(b), the Class B standard requires that seven representative samples of the biosolids that are used or disposed shall be collected. The geometric mean of the density of fecal coliform in the samples collected shall be less than either 2,000,000 MPN / g of total solids (dry weight basis) or 2,000,000 Colony Forming Units (CFU) per gram of total solids (dry weight basis). Class B biosolids should not exceed limits for As, Cd, Cr, Co, Pb, Hg, Mo, Ni, Se, Zn.

[0021] As illustrated in Figure 1, exemplary biosolids processing apparatus 10 includes biosolids source 20, greenhouse 40, conveyance 60, and biosolids disposal 80. Biosolids 11 are sequentially communicated from biosolids source 20 through greenhouse 40, and then, using conveyance 60, to biosolids disposal 80, as illustrated. Biosolids 11 at input state 21 are communicated into greenhouse 40 from biosolids source 20. Biosolids 11 are communicatedfrom greenhouse 40 to conveyance 60 in first processed state 23, as illustrated. Biosolids 1 1 are communicated from conveyance 60 to biosolids disposal 80 in second processed state 27, as illustrated. Thus, in this implementation, biosolids 11 are processed in a two-stage process wherein greenhouse 40 processes biosolids 11 from input state 21 to first processed state 23 as biosolids 11 are communicated through greenhouse 40, and conveyance 60 processes biosolids 11 from first processed state 23 to second processed state 27 as biosolids 11 are communicated by conveyance 60. Although greenhouse 40 and conveyance 60 are presented as a single greenhouse and single conveyance for explanatory purposes in this exemplary implementation, it should be recognized that greenhouse 40 and conveyance 60 may each be configured as multiple greenhouses and / or multiple conveyances, respectively, variously operated in parallel or in sequence with one another, in various other implementations.

[0022] As illustrated in Fig. 1, exemplary biosolids processing apparatus 10 further includes solar thermal collector 13 and thermal storage 17. Working fluid 15 is communicated between solar collector 13 that heats working fluid 15, thermal storage 17, and greenhouse 40 and conveyance 60. Both greenhouse 40 and conveyance 60 are heated by working fluid 15, as illustrated. Working fluid 15 may, for example, include water, various organic fluids such as oil(s) or glycol, and combinations thereof, as would be readily recognized by those of ordinary skill in the art upon study of this disclosure. Working fluid 15 comprised of oil may, for example, be heated to a temperature generally between about 200 °F (93 °C) and 600 °F (316 °C) by solar collector 13 and stored in thermal storage 17. Working fluid 15 comprised of water may, for example, be heated to a temperature generally between about 150 °F (66 °C) and 300 °F (180 °C) by solar collector 13 and stored in thermal storage 17. Working fluid 15 is communicated to greenhouse 40 at first working fluid temperature TWi and working fluid 15 is communicated to conveyance 60 at second working fluid temperature TW2, as illustrated in Fig. 1. First working fluid temperature TWi and second working fluid temperature TW2 may be either generally equal or may differ from one another, in various implementations.

[0023] Biosolids source 20 may receive biosolids and process biosolids including dewatering biosolids, such as biosolids 11, variously generated by secondary biological processes used in wastewater treatment such as an activated sludge process. In various implementations, biosolids source 20 may include sludge thickener(s), sludge digester(s), centrifuge(s), along with pump(s),piping, controls, and so forth, as would be readily understood by those of ordinary skill in the art upon study of this disclosure.

[0024] In various implementations, solar collector 13 may be formed according to any commercially available concentrating solar thermal collector technology, including parabolic dish or trough configured to heat working fluid 15 using solar energy. An exemplary solar collector 13 is the one axis parabolic solar concentrator model S20 manufactured by Rackam of Valcourt, QC, Canada. As used herein, solar collector 13 further includes non-solar energy sources such as, for example, a heat pump, a combustion heater, a resistive heater, an apparatus for heat recovery from cogeneration systems, an apparatus for waste heat recovery, and combinations thereof, as may be used to provide heat or heating as operating conditions may necessitate (e.g., when solar energy is not available).

[0025] Thermal storage 17 may be formed as an insulated tank with low-velocity quiescent upper and lower fluid manifolds to promote thermocline layer and thermal stratification to contain working fluid 15 until working fluid 15 is required for heating greenhouse 40 and conveyance 60. Working fluid 15 communicates between solar collector 13, thermal storage 17, greenhouse 40 and conveyance 60, as illustrated. Solar collector 13 in combination with thermal storage 17, greenhouse 40 and conveyance 60 may include various fluid pathways, heat exchanger(s), pump(s), gauges, fluid controls, and so forth, that cooperate operatively with the fluid pathways communicating working fluid 15, as would be readily recognized by those of ordinary skill in the art upon study of this disclosure. While Fig. 1 illustrates working fluid 15 as being communicated from solar collector 13 to thermal storage 17 and thence to greenhouse 40 and conveyance 60, it should be recognized that working fluid 15 may be recirculated at least in part, in various implementations. Such recirculation is not included for clarity of explanation. Furthermore, it should be recognized that working fluid 15 being communicated between solar collector 13, thermal storage 17, greenhouse 40 and conveyance 60 may have differing compositions, temperatures, or differing compositions and temperatures, in various implementations. For example, working fluid 15 comprised of organic fluid may be communicated between solar collector 13 and thermal storage 17 while working fluid 15 comprised of water may be communicated between thermal storage 17 and greenhouse 40 and conveyance 60 with the organic fluid exchanging heat with the water via a heat exchanger (not shown).

[0026] Figs. 2 and 3 illustrate greenhouse 40. As illustrated in Fig. 2, greenhouse 40 is formed at least in part as a dome 47 that encloses thermal floor 42 and defines interior 45. The dome 47 of greenhouse 40 preferably includes transparent material such as glass or plexiglass that allows influx of solar radiation 14 therethrough into interior 45. The transparent material may be self- supporting or may be supported, at least in part, by framework formed, for example, of steel members. In some implementations, portions of dome 47 may be formed of transparent or translucent plastic sheeting supported by a framework. Solar radiation 14 communicated through dome 47 may, at least in part, heat interior 45 to interior temperature TI.

[0027] As illustrated in Figs. 2 and 3, thermal floor 42 defines outer circumference 41 having radius Ri and inner circumference 43 having inner radius R2 that lie within interior 45. As illustrated in Fig. 2, biosolids 11 pass into greenhouse 40 through biosolids inflow 56 located on a periphery of dome 47. Biosolids inflow 56 is preferably a receiving chute having blades for breaking up biosolid clumps. Feed conveyor 52 is configured to convey biosolids 11 from biosolids inflow 56 to generally proximate pivot 58, and feed conveyor 52 cooperates with distribution conveyor 53 proximate pivot 58 to transfer biosolids 11 from feed conveyor 52 onto distribution conveyor 53. The cooperation between feed conveyor 52 and distribution conveyor 53 may include features that break clumps in biosolids 11 and otherwise prepare biosolids 11 for distribution onto thermal floor 42. Note that feed conveyor 52 remains fixed with respect to pivot 58 and biosolids inflow 56. Distribution conveyor 53 and biosolids handler 54 are located proximate one another, and rotate together in tandem over thermal floor 42 about pivot 58 located at a center of thermal floor 42, as illustrated. Distribution conveyor 53 conveys biosolids 11 generally from pivot 58 to outer circumference 41 of thermal floor 42 and then distributes biosolids 11 onto thermal floor 42 proximate outer circumference 41. Biosolids 11 falling from distribution conveyor 53 may first fall upon biosolids handler 54 and then fall upon thermal floor 42 allowing the biosolids handler 54 to aerate biosolids 11, mix biosolids 11, break up clumps of material in biosolids 11, etc. Feed conveyor 52 and distribution conveyor 53 may, for example, use a series of moveable hoppers or a conveyor belt to transfer biosolids 11. Thermal floor 42 is heated to thermal floor temperature TF by working fluid 15 at first working fluid temperature TWi to heat, at least in part, biosolids 11 disposed upon thermal floor 42 to first temperature Ti. Heating of thermal floor 42 may, at least in part, heat interior 45 to interior temperature TI. Solar radiation 14 may also heat interior 45, at least in part, to interior temperature TI.

[0028] Ventilation system 57 is disposed about a center of dome 47 and generally coincident with pivot 58 to draw ambient air into interior 45 from the exterior environment, as illustrated in Fig. 2. Ambient air then passes through interior 45 over biosolids 11 disposed upon thermal floor 42 from inner circumference 43 to outer circumference 41 and, thence, is discharged through vents 59a, 59b disposed around the periphery of dome 47 into the ambient environment to dry biosolids 11 disposed upon thermal floor 42, as illustrated. Odor control processes (not shown) may cooperate with vents 59a, 59b to control the odor of air discharged from dome 47 through vents 59a, 59b, in various implementations. Various numbers of vents, such as vents 59a, 59b, may be included in various implementations. Ventilation system 57 has a conical structure, as illustrated, configured to distribute air circumferentially. Ventilation system 57 is active and thus includes one or more fans to forcibly draw ambient air into interior 45 and to convect air within interior 45 forcibly downward to contact biosolids 11 disposed upon thermal floor 42, in this implementation. Vents, such as vents 59a, 59b, may be either active or passive, in various implementations. In certain implementations, such as during certain seasons, the airflow may be reversed with ambient air being drawn into the interior through the vents, such as vents 59a, 59b, and then discharged into the ambient environment through ventilation system 57. Ventilation system 57 may further include one or more fans (not shown) disposed within interior 45 to circulate air within interior 45. Such fans, for example, may be suspended downward from dome 47 at various locations within interior 45.

[0029] Fig. 4 illustrates portions of biosolids handler 54. In this exemplary implementation, biosolids handler 54 is configured as two open half- cylinders that extend radially across thermal floor 42 and are rotatably mounted to an axle. As the axle is rotated, the open half-cylinders scoop up and then release biosolids 11 to mix and traverse biosolids 11. Such mixing by biosolids handler 54 may break up clumps and clods of biosolids 11, mix biosolids 11, and variously reposition portions of biosolids 11 between thermal floor 42 and a surface of biosolids 11 in order to enhance heating and drying of biosolids 11. Longitudinal movement of biosolids handler 54 along rails during axial rotation traverses biosolids 11 from outer circumference 41 to inner circumference 43 as biosolids 11 are being mixed, in this implementation. An exemplary biosolids handler 54 is the Solstice Sludge Turner available from Huber SE of Berching, Germany.

[0030] Conveyance 60, as illustrated in Fig. 2, is disposed below thermal floor 42 with conveyance 60 defining conveyance first end 61 and conveyance second end 63. Conveyance 60 is heated to conveyance temperature TC by working fluid 15 at second working fluid temperature TW2 to heat, at least in part, biosolids 11 disposed upon conveyance 60 to second temperature T2 as the biosolids are conveyed from conveyance first end 61 to conveyance second end 63. Thermal floor temperature TF and conveyance temperature TC may, at least in part, generally maintain interior 45 at interior temperature TI.

[0031] In operation, biosolids 11 in input state 21 (see Table 1 below) are communicated from biosolids source 20 into greenhouse 40 through biosolids inflow 56 onto feed conveyor 52, and biosolids 11 are then transferred from feed conveyor 52 onto distribution conveyor 53. Distribution conveyor then distributes biosolids 11 onto thermal floor proximate outer circumference 41 of thermal floor 42 within greenhouse 40 while rotating clockwise (with respect to the viewpoint of Fig. 3). Biosolids 11 in input state 21 may have TS content as indicated in Table 1 below.

[0032] Biosolids handler 54 rotates clockwise (with respect to the viewpoint of Fig. 3) concurrent with and following distribution conveyor 53, in this implementation. Of course, biosolids handler 54 and portions of distribution conveyor 53 may rotate together either clockwise or counterclockwise, in various implementations. Biosolids handler 54 then mixes biosolids 11 while transferring biosolids 11 from outer circumference 41 to inner circumference 43. At inner circumference 43, biosolids 11 are communicated by gravity through one or more passages 46 at inner circumference 43 of thermal floor 42 onto conveyance first end 61 of conveyance 60. Accordingly, biosolids 11 generally describe a spiral path 91 across thermal floor 42 from outer circumference 41 to inner circumference 43, as illustrated in Fig. 3.

[0033] Working fluid 15 is heated by solar collector 13 and stored in thermal storage 17. Working fluid 15 at first working fluid temperature TWi (see Table 1) is then communicated from thermal storage 17 through interior passages within thermal floor 42 to heat biosolids 11 to first temperature Ti (see Table 1) in order to evaporate water from biosolids 11 as biosolids 11 are being transferred from outer circumference 41 to inner circumference 43. Solar energy from solar radiation 14 may also, in part, heat biosolids 11 to first temperature Ti by radiation heat transfer and by contact with air within interior 45 heated by solar radiation 14 to interiortemperature TI (see Table 1) in order to evaporate water from biosolids 1 1 as biosolids 11 are being transferred from outer circumference 41 to inner circumference 43.

[0034] Ventilation system 57 communicates ambient air into interior 54 and forces air within interior 45 at interior temperature TI downward onto surface of biosolids 11 arrayed across thermal floor 42 to evaporate water from biosolids 11. Humid air is then purged from interior 45 through vents, such as vents 59a, 59b, and may be purged either continuously or intermittently. Air may be passed through a heat exchanger as air exits through vents, such as vents 59a, 59b, with a transfer liquid absorbing heat. The transfer liquid may then cooperate with a heat exchanger disposed within ventilation system 57 to transfer heat to air flowing into interior 45 thereby recycling the heat.

[0035] Operation of ventilation system 57 and / or the vents, such as vents 59a, 59b, may be based on, for example, the interior air humidity, exterior air humidity, interior temperature TI, and / or exterior air temperature. Operation of ventilation system 57 and / or the vents may prioritize heat build-up within interior 45 followed by quickly purging humid air without removing more heat than necessary. Sensor(s) (not shown) may also trigger operation of ventilation system 57 and / or the vents in order to limit gas concentration of undesirable gas to less than a specified gas concentration wherein undesirable gas includes, for example, H2S and ammonia.

[0036] Biosolids processing apparatus 10 may be controlled so that as the solar Direct Normal Irradiance (DNI) decreases / increases due to clouds or nighttime / daytime the thermal floor temperature TF is altered to maintain an even energy load within interior 45 for continuous drying, day and night, or during cloudy periods. The heat required may be from solar collector 13 and may be supplemented by other conventional sources such as natural gas. Air being input into interior 45 may be heated to lower the dewpoint and accelerate evaporation when the outdoor humidity begins to reach the saturation point. This also allows control of conditions within interior 45 to best enhance evaporation during the cold months when the ambient air is cold.

[0037] Because water is evaporated from biosolids 11 by heating of biosolids 11 and by forced air convection by ventilation system 57 as biosolids 11 are transferred from outer circumference 41 to inner circumference 43, biosolids 11 are in first processed state 23 when biosolids 11 reach inner circumference 43.

[0038] Biosolids 11 in first processed state 23 have TS as indicated in Table 1 . Biosolids 1 1 in first processed state 23 may meet Class B standard as defined by 40 Code of Federal Regulations (CFR) Part 503, Standards for the Use of Disposal of Sewage Sludge.

[0039] First detention time Di (see Table 1) is defined as the amount of time biosolids 11 are maintained proximate first temperature Ti within greenhouse 40, and first detention time Di may be generally equivalent to the time require for biosolids 11 to traverse thermal floor 42 from outer circumference 41 to inner circumference 43 which may correspond to the time required for biosolids handler 54 to make a complete rotation around pivot 58. Thermal floor 42 may be sized and feed conveyor 52, distribution conveyor 53, and biosolids handler 54 operated to select first detention time Di. First detention time Di and first temperature Ti may be selected to produce a desired first processed state 23 of biosolids 11 given input state 21 of biosolids 11 entering greenhouse 40. Thermal floor temperature TF and interior temperature TI may be selected to produce the selected first temperature T i of biosolids 11. First working fluid temperature TWi may be selected to produce the selected thermal floor temperature TF.

[0040] Biosolids 11 in first processed state 23 are then communicated from inner circumference 43 of thermal floor 42 through passage(s) 46 onto conveyance first end 61 of conveyance 60. Accordingly, biosolids 11 proximate first end 61 of conveyance 60 are generally in first processed state 23. Passage(s) 46 may be formed as a rectangular, circular, or arcuate slot 65.

[0041] Working fluid 15 is then communicated from thermal storage 17 to conveyance 60 to heat biosolids 11 to a second temperature T2 (see Table 1) as biosolids 11 are being conveyed from conveyance first end 61 to conveyance second end 63. The second working fluid temperature TW2 (see Table 1) of working fluid 15 and the resulting conveyance temperature TC (see Table 1) of conveyance 60 are configured to heat biosolids 11 to second temperature T2 (see Table 1). An entirety of biosolids 11 may be exposed to conveyance temperature TC as the biosolids are being conveyed thereby ensuring that an entirety of biosolids 11 is heated to second temperature T2. Biosolids 11 are maintained at second temperature T2 for second detention time D2 (see Table 1) so that at least second detention time D2 is required to transfer biosolids 11 from conveyance first end 61 to conveyance second end 63. Biosolids 11 in second processed state 27 (see Table 1) are then communicated from conveyance second end 63 of conveyance 60 to biosolids disposal 80 for further processing and disposal.

[0042] Biosolids 11 in second processed state 27 may have TS as indicated in Table 1 . Second detention time D2 is defined as the amount of time biosolids 11 are maintained proximate second temperature T2 within conveyance 60, and second detention time D2 may be generally equivalent to the time required to convey biosolids 11 from conveyance first end 61 to conveyance second end 63. Conveyance 60 may be sized and operated to select second detention time D2. Second detention time D2 and second temperature T2 may be selected to produce a desired second processed state 27 of biosolids 11 from first processed state 23. Conveyance temperature TC may be selected to produce the selected second temperature T2 of biosolids 11. Second working fluid temperature TW2 may be selected to produce the selected conveyance temperature TC. Note that first detention time Di may or may not be equivalent to second detention time D2, first temperature Ti may or may not be equivalent to second temperature T2, thermal floor temperature TF may or may not be equivalent to conveyance temperature TC, and first working fluid temperature TWi may or may not be equivalent to second working fluid temperature TW2, in various implementations. First detention time Di, second detention time D2, first temperature Ti, and second temperature T2 may be selected to produce biosolids 11 with a desired second processed state 27 from biosolids 11 in input state 21 using greenhouse 40 and conveyance 60 arranged in a two-stage process.

[0043] Biosolids disposal 80 may variously treat biosolids 11 in second processed state 27, may aggregate biosolids 11 in second processed state 27 in various containers for shipment, and may otherwise handle biosolids 11 in second processed state 27 in various ways, as would be readily understood by those of ordinary skill in the art upon study of this disclosure.

[0044] Second temperature T2 and second detention time D2 may be selected so that biosolids 11 in second processed state 27 meet various standards. For example, second temperature T2 and second detention time D2 may be selected so that biosolids 11 in second processed state 27 meet, for example, the Class A standard as defined by 40 Code of Federal Regulations (CFR) Part 503, Standards for the Use of Disposal of Sewage Sludge.

[0045] In addition, heating of biosolids 11 disposed upon conveyance 60 to second temperature T2 may evaporate water from biosolids 11 as biosolids 11 are being conveyed from conveyance first end 61 to conveyance second end 63. Various ventilation equipment may be provided to flow forcibly air about conveyance 60 and dispose of the resulting humid air, for example, by ejection to the ambient environment.

[0046] Values for certain dimensions and operational parameters of various implementations of exemplary biosolids processing apparatus 10 are given in Table 1 below.

[0047] Note that the values of the dimensions and operational parameters in Table 1 are approximate, and the values of the dimensions and operational parameters in Table 1 are exemplary not limiting. Values of the dimensions and operational parameters that differ fromthose cited in Table 1 may be used in various other implementations. Note that conversions between units in Table 1 are rounded. In certain climates or seasons, the biosolids processing apparatus 10 may be batch operated with biosolids 11 being input only during daylight hours. In other climates or seasons, the biosolids processing apparatus 10 may be operated as a continuous flow process with biosolids 11 being continuously input throughout an entire 24-hour period. Thus, for example, it should be understood that the 4 wet ton / hr rate of biosolids input given in Table 1 is likely very climate and seasonally dependent and is provided only to give a sense of the general capability of an exemplary implementation of biosolids processing apparatus 10.

[0048] Exemplary process 400 illustrated in Fig. 5 may be implemented using exemplary biosolids processing apparatus 10. As illustrated in Fig. 5, process 400 is entered at step 401.

[0049] At step 405, biosolids in input state are distributed on a thermal floor of a greenhouse at an outer circumference of the thermal floor. The thermal floor is circular in shape.

[0050] At step 410, the biosolids are transferred from the outer circumference to an inner circumference as the biosolids are being mixed and heated to first temperature Ti for first detention time Di thereby transforming the biosolids from the input state into the first processed state. Heating the biosolids to first temperature Ti evaporates water from the biosolids. The thermal floor may be heated using a working fluid in order to heat the biosolids to first temperature Ti. The working fluid may be heated using a solar collector, and step 410 may be configured as a continuous flow process.

[0051] At step 415, water is evaporated from the biosolids by forced convection of air at interior temperature TI within greenhouse interior over the biosolids as the biosolids are being transferred. Air within greenhouse interior may be heated to interior temperature TI, at least in part, by solar energy captured within the greenhouse.

[0052] At step 420, water evaporated from the biosolids is removed from the greenhouse interior of the greenhouse by exchanging air within the greenhouse interior with the ambient environment. The biosolids are thus dried by steps 410, 415, which may be generally concurrent, from input state to first processed state thereby increasing TS of the biosolids as the biosolids are transferred from outer circumference to inner circumference.

[0053] At step 425, biosolids in first processed state are communicated from the inner circumference of the thermal floor through a passage onto the conveyance.

[0054] At step 430, the biosolids are heated to second temperature T2 for second detention time D2 at least in part by heating the conveyance using the working fluid while conveying the biosolids from the conveyance first end to the conveyance second end thereby transforming the biosolids from the first processed state into the second processed state. The biosolids are in second processed state at conveyance second end. Heating the biosolids to second temperature T2 for second detention time D2 evaporates water from the biosolids thus increasing the TS of the biosolids and reduces the microbial population within the biosolids at the second processed state. Second temperature T2 and second detention time D2 may be selected to cooperate to reduce the microbial population of the biosolids in second processed state. Temperature T2 and detention time D2 may be selected such that biosolids in second processed state meet certain standards such as, for example, the Class A standard as set forth by USEPA.

[0055] At step 435, the biosolids are communicated from the conveyance second end of the conveyance to biosolids disposal for further processing and disposal.

[0056] Exemplary process 400 terminates at step 471.

[0057] The foregoing discussion along with the Figures discloses and describes various exemplary implementations. These implementations are not meant to limit the scope of coverage, but, instead, to assist in understanding the context of the language used in this specification and in the claims. The Abstract is presented to meet requirements of 40 C.F.R.§ 1.72(b) only. Accordingly, the Abstract is not intended to identify key elements of the apparatus and methods disclosed herein or to delineate the scope thereof. Upon study of this disclosure and the exemplary implementations herein, one of ordinary skill in the art may readily recognize that various changes, modifications and variations can be made thereto without departing from the spirit and scope of the inventions as described herein and as defined in the following claims.

Claims

CLAIMS1. A method of biosolids processing, comprising the steps of: distributing biosolids in an input state onto an outer circumference of a thermal floor disposed within a greenhouse, the thermal floor adapted to transfer heat to the biosolids; and transforming the biosolids from the input state into a first processed state by heating the biosolids to a first temperature Ti for a first detention time Di within the greenhouse while spirally transferring the biosolids from the outer circumference of the thermal floor to an inner circumference of the thermal floor.

2. The method of claim 1, further comprising the steps of communicating the biosolids in the first processed state from the thermal floor onto a conveyance first end of a conveyance; and heating the biosolids to a second temperature T2 for a second detention time D2 while conveying by the conveyance the biosolids from the conveyance first end to a conveyance second end thereby transforming the biosolids from the first processed state into a second processed state.

3. The method of claim 1, wherein the thermal floor is adapted to transfer heat to the biosolids from a working fluid being communicated within the thermal floor.

4. The method of claim 2, wherein the conveyance is adapted to transfer heat from a working fluid to the biosolids while conveying the biosolids.

5. The method of claim 1, further comprising the step of: mixing the biosolids while spirally transferring the biosolids from the outer circumference of the thermal floor to the inner circumference of the thermal floor.

6. The method of claim 1, further comprising the step of: evaporating water from the biosolids within the greenhouse at least in part using forced air convection.

7. The method of claim 2, wherein the biosolids in the second processed state meet a standard selected from a total solids standard and a microbial population standard.

8. The method of claim 7, wherein the total solids standard requires a total solids of at least about 75% for digested biosolids and 90% for non-digested biosolids.

9. The method of claim 7, wherein the microbial population standard is selected from a group consisting of: i) fecal coliform is belowl,000 MPN / g of dry solids; ii) Salmonella is measured at less than 3 MPN / 4g of dry solids; iii) less than 2,000,000 MPN / g of total solids (dry weight basis); and iv) less than 2,000,000 CFU / g of total solids (dry weight basis).

10. A biosolids processing apparatus, comprising: a thermal floor disposed within a greenhouse, the thermal floor being circular and defining an outer circumference and an inner circumference, the thermal floor adapted to transfer heat to the biosolids from a working fluid communicated through the thermal floor to heat the biosolids to a first temperature Ti for a first detention time Di in order to transform the biosolids from an input state proximate the outer circumference into a first processed state proximate the inner circumference; a distribution conveyor having a first end pivotably mounted at a center of the thermal floor and a second end for rotating along the outer circumference of the thermal floor, wherein the distribution conveyor is adapted to transfer biosolids in the input state onto the outer circumference of the thermal floor; and a biosolids handler that cooperates with the thermal floor to spirally transfer the biosolids from the outer circumference to the inner circumference, the biosolids handler having a first end pivotably mounted at the center of the thermal floor and a second end for rotating along the outer circumference of the thermal floor in tandem with the second end of the distribution conveyor.11 . The apparatus of claim 10, wherein the biosolids handler mixes the biosolids as the biosolids are spirally transferred from the outer circumference of the thermal floor to the inner circumference of the thermal floor.

12. The apparatus of claim 10, further comprising: a conveyance defining a conveyance first end and a conveyance second end, the conveyance first end mounted beneath the inner circumference of the thermal floor and adapted to receive biosolids in the first processed state from one or more openings through the thermal floor along the inner circumference.

13. The apparatus of claim 12, wherein the conveyance is adapted to transfer heat from the working fluid to biosolids received by the conveyance in order to heat the biosolids to a second temperature T2 for second detention time D2 as the biosolids are being conveyed by the conveyance from the conveyance first end to the conveyance second end to transform the biosolids from the first processed state into a second processed state.

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