High-rate anaerobic digestion of sewage sludge using anaerobic dynamic membrane bioreactor under various sludge composition and organic loading rates

Recyclable cation exchange resin-driven fermentation of waste activated sludge in sequential batch-parallel pattern: long-term resin/regenerant recycle stability and triple driving mechanisms

Anaerobic acidogenic fermentation has been posited as a preferable technology for waste activated sludge management, whereas the inefficient hydrolysis, inadequate metabolism and disordered microbiota still existed as three fermentability limitations. The existing solutions addressed single limitation while consuming substantial chemicals/energy, thereby restraining technological dissemination. Innovatively, the recyclable cation exchange resin (CER) is a promising approach for synchronously overcoming these fermentability limitations and reducing chemicals/energy costs from sludge-native metal removal perspective; however, it has been rarely reported. This study pioneered a recyclable CER-driven sludge fermentation in continuous CER and regenerant reuse scene, taking comprehensive insights into long-term performance and multiple mechanisms. The CER induced speciation conversion and stepwise removal of structural metals from sludge, especially organic-binding and residual Ca&Mg, which played triple driving contributions: (1) breaking metal-bridging sites and hydrogen bonds disentangled protein molecules for raising electronegative repulsion and flocculation energy barrier, causing synergic extracellular and intracellular hydrolysis (up to 30.05 %); (2) liberating endogenous redox mediators from metal-complexations for assisting electron shuttle and extracellular respiration, which metabolic electron transfer activity by 1.58 times; (3) triggering "bacteria screening" through sensitive methanogen inhibition and tolerant acidogens growth towards maximum acidogenic eco-functions. Such fermentability breakthroughs greatly promoted short-chain fatty acids (superior carbon sources) accumulation by average 2.52 folds while declining sludge solid by 55.87 %. The NaCl regeneration thoroughly restored CER active sites and eluted pollutant blockages, with negligible capability loss ≤ 3.53 % in 18-cycle operations, which stabilized acidogenic performances during 72-day fermentation (RSD ≤ 7.88 %). The fermentative products presented as high-quality carbon sources with abundant carbon and absent nitrogen, owing to CER-mediated NH4+ exchange. Innovative batch-parallel operation was established in engineering strategy, offering 409.49 CNY/ton SS income. The findings provided mechanism framework linking sludge fermentability with native metal functions.

Enhanced performance and economic feasibility of sewage sludge digestion using a two-stage anaerobic digestion with a dynamic membrane and alkaline-thermal pretreatment

This study suggests a high-rate sewage sludge anaerobic digestion (AD) process. An alkaline-thermal pretreatment and a dynamic membrane (DM) were used to enhance AD efficiency and economic feasibility in a two-stage system. The effect of pretreatment on volatile fatty acid (VFA) production in the acidogenic phase was investigated at various hydraulic retention times (HRT). After optimizing the acidogenic phase condition (HRT of 3 days), single- and two-stage AD processes with DM modules were operated simultaneously to compare performance. The highest methane production rates of 0.69 L/L/d for single-stage AD and 1.10 L/L/d for two-stage AD were observed at a total HRT of 12 days. Phase separation enhanced the growth of acetoclastic methanogens. A techno-economic analysis showed that the two-stage AD system would achieve a positive net present value within 2 years. This study demonstrated the feasibility of high-rate AD systems for sewage sludge using DM, alkaline-thermal pretreatment, and phase separation.

Feasibility of biogas upgrading at a WWTP after pre-treatment application: Techno-economic assessment validation with pilot test data

Improving the efficiency of anaerobic digestion (AD) of sewage sludge (SS) is a critical step toward the achievement of energy neutrality in wastewater treatment plants (WWTPs), as required by the European Green Deal. This study used a comparative techno-economic assessment (TEA) to evaluate the feasibility of producing biomethane, at a WWTP, through upgrading biogas with a double-stage permeation membrane plant. The biogas was originally generated from the AD of a mixture of primary sludge (PS) and either raw or pre-treated waste activated sludge (WAS), where biological or thermo-alkali pre-treatments were applied to increase the WAS intrinsic low degradability. The TEA was supported by the results of pilot-scale tests, carried out on WAS, which mimicked (i) a traditional mesophilic AD process; (ii) a two-stage AD process, where a temperature-phased anaerobic digestion (TPAD, 3 days, 55 °C + 20 days, 38 °C) was performed to biologically pre-treat WAS; (iii) a traditional mesophilic AD process preceded by a thermo-alkali (4 g NaOH/100 g TS, 90 °C, 90 min) pre-treatment. The TEA was carried out in two phases. In the first, the minimum size of the WWTP capable of making the costs necessary for the implementation of the biogas upgrading plant equal to the revenues coming from selling biomethane (at 62 €/MWh) in 10 years was calculated in the absence of pre-treatments. It resulted of 500,000 equivalent inhabitants (e.i.). In the second phase, for the WWTP size found previously, the effect of either biological or thermo-alkali pre-treatments on the economic balance was evaluated, that is the gain (or the loss) associated to the selling of biomethane, compared to the reference price of 62 €/MWh. It was found that the TPAD increased the biogas productivity by only 23.6%, too little to compensate the amount of heat necessary for the pre-treatment and the purchase cost of the additional reactor. Conversely, the thermo-alkali pre-treatment, which enhanced the WAS biogas productivity by 110%, increased the biomethane revenues by approx. 10 €/MWh, compared to the scenario without pre-treatments. This study offers useful data to WWTP managers who want to introduce WAS pre-treatments, combined with interventions for biogas upgrading, in a new or existing sludge line of a WWTP.

Separation of nutrients from SCFAs with a dynamic membrane in a sludge anaerobic fermenter

The complexity and high cost to separate and recover short chain fatty acids (SCFAs), ammonium ions, and phosphates in the sludge fermentation liquid hinder the application of sludge anaerobic fermentation. In this study, an interesting phenomenon was found in a sludge anaerobic fermenter with a dynamic membrane (DM) which could not only enhance SCFAs production but also retain most SCFAs in fermenter. The separation factor of DM for NH3-N/SCFAs and PO43-/SCFAs throughout the DM development were about 40 and 80, respectively. Analysis reveals that rejection of SCFAs by DM could not be simply correlated to molecular weight or membrane pore size. The rejection mechanisms might be dominated by Donnan rejection. In addition, biodegradation in the DM may also have contribution. Findings of this study suggest the potential of DM as an economical technology for nutrients and SCFAs recover.

Energy and nutrient recovery from municipal and industrial waste and wastewater-a perspective

This publication highlights the latest advancements in the field of energy and nutrient recovery from organics rich municipal and industrial waste and wastewater. Energy and carbon rich waste streams are multifaceted, including municipal solid waste, industrial waste, agricultural by-products and residues, beached or residual seaweed biomass from post-harvest processing, and food waste, and are valuable resources to overcome current limitations with sustainable feedstock supply chains for biorefining approaches. The emphasis will be on the most recent scientific progress in the area, including the development of new and innovative technologies, such as microbial processes and the role of biofilms for the degradation of organic pollutants in wastewater, as well as the production of biofuels and value-added products from organic waste and wastewater streams. The carboxylate platform, which employs microbiomes to produce mixed carboxylic acids through methane-arrested anaerobic digestion, is the focus as a new conversion technology. Nutrient recycling from conventional waste streams such as wastewater and digestate, and the energetic valorization of such streams will also be discussed. The selected technologies significantly contribute to advanced waste and wastewater treatment and support the recovery and utilization of carboxylic acids as the basis to produce many useful and valuable products, including food and feed preservatives, human and animal health supplements, solvents, plasticizers, lubricants, and even biofuels such as sustainable aviation fuel.

ONE-SENTENCE SUMMARY

Multifaceted waste streams as the basis for resource recovery are essential to achieve environmental sustainability in a circular economy, and require the development of next-generation waste treatment technologies leveraging a highly adaptive mixed microbial community approach to produce new biochemicals, biomaterials, and biofuels from carbon-rich organic waste streams.