Employing micro-aeration in anaerobic digestion of poultry litter and wheat straw: Batch kinetics and continuous performance

In-situ intermittent micro-aeration in food waste and sewage sludge anaerobic co-digestion: Performance, stability, and microbial dynamics

Anaerobic co-digestion (AcoD) of sewage sludge (SS) with food waste (FW) is a practical approach in urban areas due to spatio-temporal availability of these co-substrates. While micro-aeration could enhance hydrolysis and control acidification during mono-digestion, the effects of micro-aeration on AcoD remains unclear. This study explored the influence of oxidation-reduction potential (ORP)-based in-situ micro-aeration on AcoD performance of SS and FW. Although mono-digestion of FW failed due to acidification and micro-aeration of SS was unstable due to high solids content and viscosity, micro-aeration improved specific biogas and methane yields by 21.1 % and 13.1 %, respectively, at the FW:SS ratio of 60:40 ((volatile solids (VS) basis). This improvement was observed at an organic loading rate of 2.25 g VS/L·d and alkalinity below 5000 mg CaCO3/L. The observed positive effect of micro-aeration was accompanied by changes in relative abundance of Aminicenantes. Functional analysis suggested that AcoD was driven by homoacetogenesis and acetoclastic methanogenesis.

Enhanced nutrient recovery from anaerobically digested poultry wastewater through struvite precipitation by organic acid pre-treatment and seeding in a bubble column electrolytic reactor

Limited mineralization of organic phosphorus to phosphate during the anaerobic digestion process poses a significant challenge in the development of cost-effective nutrient recovery strategies from anaerobically digested poultry wastewater (ADPW). This study investigated the influence of organic acids on phosphorus solubilization from ADPW, followed by its recycling in the form of struvite using a bubble column electrolytic reactor (BCER) without adding chemicals. The impact of seeding on the efficiency of PO43- and NH3-N recovery as well as the size distribution of recovered precipitates from the acid pre-treated ADPW was also evaluated. Pre-treatment of the ADPW with oxalic acid achieved complete solubilization of phosphorus, reaching ∼100% extraction efficiency at pH 2.5. The maximum removal efficiency of phosphate and ammonia-nitrogen from the ADPW were 88.9% and 90.1%, respectively, while the addition of 5 and 10 g/L struvite seed to the BCER increased PO43- removal efficiency by 9.6% and 11.5%, respectively. The value of the kinetic rate constant, k, increased from 0.0176 min-1 (unseeded) to 0.0198 min-1, 0.0307 min-1, and 0.0375 min-1 with the seed loading rate of 2, 5, and 10 g/L, respectively. Concurrently, the average particle size rose from 75.3 μm (unseeded) to 82.1 μm, 125.7 μm, and 148.9 μm, respectively. Results from XRD, FTIR, EDS, and dissolved chemical analysis revealed that the solid product obtained from the recovery process was a multi-nutrient fertilizer consisting of 94.7% struvite with negligible levels of heavy metals.

Microaerobic condition as pretreatment for improving anaerobic digestion: A review

Pretreatment of waste before anaerobic digestion (AD) has been extensively studied during the last decades. One of the biological pretreatments studied is the microaeration. This review examines this process, including parameters and applications to different substrates at the lab, pilot and industrial scales, to guide further improvement in large-scale applications. The underlying mechanisms of accelerating hydrolysis and its effects on microbial diversity and enzymatic production were reviewed. In addition, modelling of the process and energetic and financial analysis is presented, showing that microaerobic pretreatment is commercially attractive under certain conditions. Finally, challenges and future perspectives were also highlighted to promote the development of microaeration as a pretreatment before AD.

Effect of air mixing on high-solids anaerobic digestion of cow manure: Performance and mechanism

This study aimed to further investigate the effect of air mixing on the performance of a high-solids anaerobic digestion system and reveal its underlying mechanisms via analyses of carbon conversion, microbial communities and key functional genes. When the air mixing intensity was 12.5, 37.5 and 62.5 mL/(L‧min), compared with the anaerobic digestion without air mixing, the methane yield was increased by 6 %, 13 % and 6 %, respectively. The improved performance was partly attributed to the increased hydrolysis rate of macromolecular substances by 5 %-16 % and carbon recovery in the form of methane by 6 %-7% compared with the controls. Functional flora (Magnetospirillum, Synergistaceae) and hydrolytic metabolism-related enzymes (cellulose, α-amylase) demonstrated higher abundance under air mixing condition, thus promoting the degradation of organic matter and methane production. This work provides some new insights into the use of air mixing to improve anaerobic digestion of high-solids waste.