Improving bioenergy recovery from municipal wastewater with a novel cloth-filter anaerobic membrane bioreactor

Martins Dias, Neriamara

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https://hdl.handle.net/2142/113942 Copy

Description

Title

Improving bioenergy recovery from municipal wastewater with a novel cloth-filter anaerobic membrane bioreactor

Author(s)

Martins Dias, Neriamara

Issue Date

2021-08-17

Director of Research (if dissertation) or Advisor (if thesis)

• Gates, Richard S
• Schideman, Lance C

Committee Member(s)

• Martin-Ryals, Ana D
• Sharma, Brajendra Kumar

Department of Study

Engineering Administration

Discipline

Agricultural & Biological Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• AnMBR: Cloth Filter: Energy
• Ion Exchange
• Wastewater: Anaerobic Digestion
• Coagulation

Abstract

Municipal wastewater treatment plants across the USA are estimated to consume 30 billion kWh per year, or about 1-3% of the country's electricity demand (Pabi et al., 2013). That equates to about $2 billion in annual electric costs and accounts for up to 40% of the annual operating budget of a typical wastewater plant (Lemar and De Fontaine, 2017). This occurs because current wastewater treatment relies primarily on the conventional activated sludge process (CAS) for aerobic degradation of organics into carbon dioxide (CO2), which is a double negative for energy efficiency. It dissipates the organic energy content of wastewater and requires substantial energy input for aeration. Anaerobic membrane bioreactors (AnMBRs) have been proposed as a more sustainable approach than CAS to manage the organics in wastewater because they eliminate the need for aeration and convert organics into a renewable energy resource (methane). However, when treating low-strength wastewaters, the high energy demand for membrane fouling control and the inability to remove nutrients, such as nitrogen and phosphorus, become critical limitations to using AnMBRs. This study aimed to develop and evaluate the performance of a novel anaerobic wastewater treatment train that uses a cloth-filter AnMBR (CFAnMBR) to increase bioenergy recovery compared to CAS and improve energy efficiency compared to current AnMBR technology. While the CFAnMBR can provide an effluent that meets most discharge requirements, it still requires an additional ammonia removal process to meet typical wastewater discharge standards. This study investigates the use of ion exchange to capture ammonia for subsequent conversion to hydrogen via electrolysis. The new CFAnMBR system developed for this study was pilot tested at a local wastewater treatment plant for 150 days treating primary influent under psychrophilic conditions (0°C – 20°C). The CFAnMBR demonstrated a very low energy demand of 0.0087 kWh/m3 for fouling control, which is 97% lower than the average value reported for other pilot AnMBRs treating municipal wastewater. The observed tradeoff was reduced effluent water quality in terms of COD removal efficiency (66 %) and TSS concentration (29 mg/L) when compared to conventional AnMBRs. However, it was demonstrated that an in-line coagulation-flocculation process could improve the CFAnMBR performance and provide effluent water quality comparable to CAS in terms of suspended solids, organics, and phosphorus removal. With the addition of 100 mg/L of FeCl3, the CFAnMBR achieved average effluent concentrations of 15 mg/L for TSS, 0.07mg/L for TP, and 89 mg/L for COD (29 mg/L for BOD). The new CFAnMBR system achieved a methane yield of 310 mL CH4/g CODremoved during operation under an organic loading rate of 0.8± 0.2 g COD/L-day, representing good performance compared to other pilot AnMBR processes. However, when the temperature dropped below 10℃, a significant fraction of the methane produced (46%) was dissolved in the permeate. Thus, a strategy to recover dissolved methane must be incorporated with a CFAnMBR system to improve net energy production during cold months and keep the methane – a potent greenhouse gas - from escaping to the atmosphere. Using ion exchange columns downstream, the CFAnMBR showed good potential for ammonia recovery from permeate. Specifically, a natural zeolite (clinoptilolite) and two synthetic ion exchange resins (Purolite SSTC60 and Purolite C160) achieved an average effluent concentration of 1 mg/L TAN after 60, 118, and 107 bed volumes (BV), respectively. Alkaline regeneration of these adsorbents recovered more than 78% of the ammonia captured and produced a concentrated sidestream of ammonia with over 1000 mg /L TAN. Although this process must be optimized to be feasible in full-scale applications, these results are promising for integrating ammonia electrolysis for brine recycling and energy generation. All in all, the overall energy demand for the removal of organics and nutrients in the novel anaerobic wastewater treatment train used in this study was estimated to be 0.162 kWh/m3 of treated wastewater. The electrical energy production from methane was 0.210 kWh/m3, resulting in a positive net energy balance of 0.0481 kWh/m3. By comparison, a typical CAS process with sidestream anaerobic digestion is estimated to require an energy input of 0.535 kWh/m3 and generate 0.12 kWh/m3 of electrical energy, resulting in a negative net energy balance of 0.41kWh/m3. These results show an opportunity to shift the municipal wastewater treatment paradigm from a significant net energy consumer to a net energy producer.

Graduation Semester

2021-12

Type of Resource

Thesis

Permalink

http://hdl.handle.net/2142/113942

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Copyright 2021 Neriamara Martins Dias

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