Evaluation of biochar addition and circulation control strengthening measures on efficiency and microecology of food waste treatment in anaerobic reactor

Biochar mediated high-rate anaerobic bioreactors: A critical review on high-strength wastewater treatment and management

Treatment of high-strength wastewater is critical for the aquatic environment and receiving water bodies around the globe. Untreated or partially treated high-strength wastewater may cause severe damage to the existing water bodies. Various high-rate anaerobic bioreactors have been developed in the last decades for treating high-strength wastewater. High-rate anaerobic bioreactors are effective in treating industrial wastewater and provide energy in the form of methane as well. However, the physical or chemical properties of high-strength industrial wastewater, sometimes, disrupt the functioning of a high-rate anaerobic bioreactor. For example, the disintegration of granular sludge in up flow anaerobic sludge blanket reactor or membrane blocking in an anaerobic membrane bioreactor are the results of a high-strength wastewater treatment which hamper the proper functioning and may harm the wastewater treatment plant economically. Biochar, if added to these bioreactors, may help to alleviate the ill-functioning of high-rate anaerobic bioreactors. The primary mechanisms by biochar work in these bioreactors are direct interspecies electron transfer, microbial immobilization, or gene level alternations in microbial structure. The present article explores and reviews the recent application of biochar in a high-rate anaerobic bioreactor treating high-strength industrial wastewater.

Advances, trends and challenges in the use of biochar as an improvement strategy in the anaerobic digestion of organic waste: a systematic analysis

A recently strategy applied to anaerobic digestion (AD) is the use of biochar (BC) obtained from the pyrolysis of different organic waste. The PRISMA protocol-based review of the most recent literature data from 2011-2022 was used in this study. The review focuses on research papers from Scopus® and Web of Knowledge®. The review protocol used permits to identify 169 articles. The review indicated a need for further research in the following challenges on the application of BC in AD: i) to increase the use of BC in developing countries, which produce large and diverse amounts of waste that are the source of production of this additive; ii) to determine the effect of BC on the AD of organic waste under psychrophilic conditions; iii) to apply tools of machine learning or robust models that allow the process optimization; iv) to perform studies that include life cycle and technical-economic analysis that allow identifying the potential of applying BC in AD in large-scale systems; v) to study the effects of BC on the agronomic characteristics of the digestate once it is applied to the soil and vi) finally, it is necessary to deepen in the effect of BC on the dynamics of nitrogen and microbial consortia that affect AD, considering the type of BC used. In the future, it is necessary to search for new solutions in terms of the transport phenomena that occurs in AD with the use of BC using robust and precise mathematical models at full-scale conditions.

Hydrothermal carbonization of food waste: Process parameters optimization and biomethane potential evaluation of process water

Food waste (FW) is one of the major biomasses produced in large quantities in urban areas, which contributes to more than one-third of global greenhouse gas emissions. FW must be properly managed to minimize its environmental consequences. Hydrothermal carbonization (HTC) of FW is a promising technology compared to conventional methods. The objective of the present study is to maximize the mass yield (MY), higher heating value (HHV) and energy yield (EY) of FW by optimizing the operational variables of HTC process. Additionally, process water generated during HTC of FW under optimal conditions was evaluated for methane yield using anaerobic digestion. To optimize the HTC process, three operational variables, including solid-to-liquid (S/L) ratio, temperature, and reaction time, were manipulated using response surface methodology (RSM). According to RSM studies, the optimum operating conditions are 198.5 °C for 150 min with a 0.2 S/L ratio, resulting in MY, HHV and EY as 62.5%, 21.24 MJ/kg and 81.71%, respectively. Proximate and elemental analysis for the hydrochars synthesized at various operating conditions reveals that the temperature and reaction time have a significant impact on fixed carbon and carbon percentage. The anaerobic digestion results showed that the combination of process water and hydrochar, yielded a maximum cumulative methane production of 298.5 ± 16.34 mL/g COD. To mimic methane production, the modified Gompertz model was utilized. Thus, this finding contributes towards the commercialization of the HTC process to produce solid fuel (hydrochar) and provides a way to find an alternative energy source that enhances the HTC process and tackles the problem of process water disposal.

Effects of upward flow rate and modified biochar location on the performance and microecology of an anaerobic reactor treating kitchen waste

Increasing the value of food waste through anaerobic digestion is an attractive strategy. Meanwhile, the anaerobic digestion of kitchen waste also faces some technical challenges. In this study, four EGSB reactors were equipped with Fe-Mg-chitosan bagasse biochar at different locations, and the reflux pump flow rate was increased to change the upward flow rate of the reactor. The effects of adding modified biochar at different locations under different upward flow rate on the efficacy and microecology of anaerobic reactors treating kitchen waste were investigated. Results showed that Chloroflexi was the dominant microorganism when the modified biochar was added to the lower, middle, and upper parts of the reactor and mixed in the reactor, accounting for 54%, 56%, 58%, and 47%, respectively, on day 45. With the increased upward flow rate, the abundance of Bacteroidetes and Chloroflexi increased, while Proteobacteria and Firmicutes decreased. It was worth noting that the best COD removal effect was achieved when the anaerobic reactor upward flow rate was v2 = 0.6 m/h and the modified biochar was added in the upper part of the reactor, during which the average COD removal rate reached 96%. In addition, mixing modified biochar throughout the reactor while increasing the upward flow rate provided the greatest stimulus for the secretion of tryptophan and aromatic proteins in the sludge extracellular polymeric substances. The results provided a certain technical reference for improving the efficiency of anaerobic digestion of kitchen waste and scientific support for the application of modified biochar to the anaerobic digestion process.