A compound enzyme as an additive to a continuous anaerobic dynamic membrane bioreactor for enhanced lignocellulose removal from codigestion: Performance, membrane characteristics and microorganisms.

To explore the enzyme-enhanced strategy of a continuous anaerobic dynamic membrane reactor (AnDMBR), the anaerobic codigestion system of food waste and corn straw was first operated stably, and then the best combination of compound enzymes (laccase, endo-ß-1,4-glucanase, xylanase) was determined via a series of batch trials. The results showed that the methane yield (186.8 ± 19.9 mL/g VS) with enzyme addition was 12.2 % higher than that without enzyme addition. Furthermore, the removal rates of cellulose, hemicellulose and lignin increased by 31 %, 36 % and 78 %, respectively. In addition, dynamic membranes can form faster and more stably with enzyme addition. The addition of enzymes changed the structure of microbial communities while maintaining sufficient hydrolysis bacteria (Bacteroidetes), promoting the proliferation of Proteobacteria as a dominant strain and bringing stronger acetylation ability. In summary, the compound enzyme strengthening strategy successfully improved the methane production, dynamic membrane effect, and degradation rate of lignocellulose in AnDMBR.

A new substrate equalization method for optimizing the influent conditions and fluid flow patterns of a multifed upflow anaerobic sludge blanket reactor with mature anammox granules.

To improve nitrogen removal efficiency (NRE) and achieve homogenous distribution of anammox sludge and substrate, a new substrate equalization theory and a cumulative overload index was proposed for multifed upflow anaerobic sludge bed (MUASB) reactors with mature anammox granules. The performance and flow patterns of MUASB reactors were investigated under various influent conditions. The results showed that the nitrogen removal performance and stability of MUASB reactors could be optimized by minimizing the cumulative load. The NRE gradually increased from 83.3 ± 2.2 %, 86.8 ± 4.2 % to 89.3 ± 4.1 % and 89.7 ± 1.6 % in feeding flow tests and feeding port tests, respectively. Furthermore, the flow patterns were compared based on residence time distribution and computational fluid dynamics, indicating that a better equilibrium distribution of microorganisms and substrates could be achieved in the MUASB reactors under the lowest cumulative load. Therefore, substrate equalization theory can be used to optimize the nitrogen removal performance of MUASB reactors with low-carbon footprints.

Long-term in-situ starvation and reactivation of co-digestion with food waste and corn straw in a continuous AnDMBR: Performance, sludge characteristics, and microorganism community.

To explore the effects of in-situ starvation and reactivation in a continuous anaerobic dynamic membrane reactor (AnDMBR), the anaerobic co-digestion system of food waste and corn straw was firstly start-up and stability operated, and then stopped feeding substrate approximately 70 days. After long-term in-situ starvation, the continuous AnDMBR was reactivated using the same operation conditions and organic loading rate as the continuous AnDMBR used before in-situ starvation. Results shown that the anaerobic co-digestion of corn straw and food waste in the continuous AnDMBR can resume stable operation within 5 days, and the corresponding methane production of 1.38 ± 0.26 L/L/d was completely returned to the methane production before in-situ starvation (1.32 ± 0.10 L/L/d). Through analysis of the specific methanogenic activity and key enzyme activity of the digestate sludge, only the acetic acid degradation activity of methanogenic archaea can be partially recovered, however, the activities of lignocellulose enzyme (lignin peroxidase, laccase, and endoglucanase), hydrolase (α-glucosidase) and acidogenic enzyme (acetate kinas, butyrate kinase, and CoA-transferase) can be fully recovered. Analysis of microorganism community structure using metagenomic sequencing technology showed that starvation decreased the abundance of hydrolytic bacteria (Bacteroidetes and Firmicutes) and increased the abundance of small molecule-utilizing bacteria (Proteobacteria and Chloroflexi) due to lack of substrate during the long-term in-situ starvation stage. Furthermore, the microbial community structure and key functional microorganism still maintained and similar with that of starvation final stage even after long-term continuous reactivation. The reactor performance and sludge enzymes activity in the continuous AnDMBR co-digestion of food waste and corn straw can be well reactivated after long-term in-situ starvation, even though the microbial community structure can not be recovered to the initiating stage.

Comparative study of the effect of loading increments on the mesophilic codigestion of waste activated sludge and food waste: Reactor performance, stability analysis, and microbial community.

The performance and stability of mesophilic codigestion of waste activated sludge (WAS) and food waste (FW) were compared in two parallel, continuously stirred tank reactors using high- and low-magnitude loading increments for the loading regimes. The results indicated that a high methane (CH4) production of 6.98 L L-1·d-1 was realized without volatile fatty acid accumulation via low-magnitude loading increments at a high loading of 26.5 g-COD·L-1·d-1, and this system was more stable and achieved a higher efficiency than the codigestion system that used high-magnitude loading increments at similar loading and operating conditions. Furthermore, higher CH4 yields of 258-334 mL-CH4·g-COD-1, TCOD removal efficiencies of 64-79%, conversion ratios of 62-88%, and methanogenic activities of 0.37-0.40 g-CH4-COD·g-VS-1·d-1 were consistently maintained via the low-magnitude loading increments during the high-rate period. High abundances of the phyla Firmicutes (63.3%) and genus Methanosarcina (94.5%) contributed to the high rates and stable operating conditions of the mesophilic system for WAS and FW codigestion using low-magnitude loading increments.