Combined UASB Reactor and Anaerobic Digester for Sub-Mesophilic Sewage
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Solution Overview
Problem
Current wastewater treatment systems, such as Imhoff tanks, pulsating UASB reactors, and two-stage UASB-digester devices, face challenges in efficiently treating unsettled sewage at sub-mesophilic temperatures (≤15°C) due to low hydrolysis rates, sludge retention issues, and high energy consumption, especially with temperature fluctuations between summer and winter.
Innovation Solution
A one-stage combined UASB reactor-anaerobic digester system with a non-heated digester located below the UASB reactor, utilizing a pulsating wastewater injection and mixing device, and a baffle sloping partition for sludge recirculation, allowing for efficient treatment of unsettled sewage without external heating and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional UASB reactor is used for treating unsettled sewage at sub-mesophilic temperatures, then the system structure is simple, but the treatment efficiency is low due to insufficient hydrolysis of entrapped solids
Solution Approach 1:
The reactor is divided into two distinct functional zones: an upper UASB reactor chamber for wastewater treatment and a lower solids anaerobic digester chamber for hydrolysis of entrapped solids. This segmentation allows each zone to perform its specific function optimally, with the lower chamber providing enhanced hydrolysis capability that conventional single-chamber UASB reactors lack.
Solution Approach 2:
The solids anaerobic digester chamber is nested within the UASB reactor structure, positioned below the main reactor chamber. The baffle sloping partition creates a nested configuration where the lower digester chamber is integrated into the overall reactor footprint, allowing the system to maintain compactness while adding the hydrolysis function.
2Productivity
If a two-stage UASB-digester device with external heating is used, then the treatment efficiency improves, but the energy consumption increases significantly
Solution Approach 1:
The lower solids anaerobic digester chamber operates at sub-mesophilic temperatures without external heating, utilizing the natural temperature of the incoming wastewater. The system self-regulates the thermal conditions for hydrolysis, eliminating the need for energy-intensive heating equipment while maintaining effective treatment through the extended residence time in the lower chamber.
Solution Approach 2:
The system changes the temperature parameter approach by rejecting the conventional mesophilic temperature range (30-40°C) in favor of sub-mesophilic operation (≤15°C). This parameter change allows the lower digester chamber to function effectively without heating, as the extended retention time compensates for the lower reaction rates, thereby reducing energy consumption while maintaining treatment efficiency.
3Ease of operation
If a pulsating UASB reactor with external feeding tank is used, then the mixing intensity increases, but the device complexity and footprint increase
Solution Approach 1:
The pulsating mixing function is merged with the wastewater feeding operation. The same external feeding tank that supplies wastewater to the upper reactor chamber also serves as the mixing vessel, eliminating the need for separate mixing equipment. The pulsating flow generated during feeding automatically mixes the contents of the lower digester chamber, achieving effective mixing without additional device complexity.
Solution Approach 2:
The external feeding tank is given multiple functions: it serves as both the wastewater supply vessel and the mixing chamber for the lower solids digester. This multi-functionality reduces the overall number of components needed in the system, maintaining effective mixing while minimizing device complexity and footprint.
4Productivity
If the sludge retention time is increased to improve hydrolysis, then the treatment efficiency improves, but the reactor volume increases
Solution Approach 1:
The system extends the retention time dimension by creating a vertical stacking of functional zones. The lower solids anaerobic digester chamber provides an additional vertical space for extended residence time, allowing sludge to remain in the system longer for hydrolysis without increasing the horizontal footprint. This dimensional approach to retention time allows efficient hydrolysis within a compact volume.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system achieves optimal soluble COD removal, low excess sludge production, and increased sludge retention time, promoting stable microbial communities and adapting to temperature fluctuations, thus enhancing treatment efficiency and reducing operational costs.
Implementation Method 1
configured to separate the upper UASB reactor chamber from the lower anaerobic digester chamber, and to collect biogas generated in the anaerobic digester chamber
Implementation Method 2
a gas-lift pump, a gas-sludge separator, and a sludge recycling pipe. The gas-lift pump elevates the sludge from the anaerobic digester chamber to the gas-sludge separator, with the energy provided by the biogas produced in the digester chamber
Implementation Method 3
an external pulse wastewater injection and mixing device having a feeding tank, configured to feed and mix the UASB reactor chamber by pulses, making the influent pass through the sludge bed of the UASB reactor chamber
Implementation Method 4
a second chamber is in the lower section of the tank and it is a non-heated anaerobic digester chamber... which is configured to receive and hydrolyze the entrapped solids which accumulate in the sludge bed of the upper UASB reactor chamber
Implementation Method 5
configured to receive and hydrolyze the entrapped solids which accumulate in the sludge bed
Implementation Method 6
the sludge recycling pipe sends the sludge from the gas-sludge separator to the pulse feeding tank by gravity
Implementation Method 7
a first chamber is in the upper section of the tank (also named upper chamber), and it is a UASB reactor chamber having a sludge bed at the lower part of the chamber, a three-phase separator at the upper part of the chamber
Data Source
Figure 1a~1c
Figure 2
Figure 3
AI summary
The present invention relates to a one-stage device for treating wastewater, such as unsettled sewage, specially wastewater having sub-mesophilic temperatures and/or showing high fluctuations of temperatures over the year, the device being essentially made of a combination of a pulsating UASB reactor with a non-heated solids anaerobic digester located below the UASB reactor, comprising a baffle sloping partition element connecting both chambers; in such a way that the sludge produced during the process inside the UASB reactor is settled downwards to the digester, recycled and sent to the UASB reactor by a gas-lift pump that operates with the biogas generated in the anaerobic digester. The UASB reactor comprises a mixing and injecting device of wastewater that works by pulses, and that not only feeds and mixes the reactor, but it also mixes the sludge bed of the digester, in different operational modes. The invention also discloses the method for treating wastewater.