Enzymatic pretreatment mitigates the dissemination of antibiotic resistance genes via regulating microbial populations and gene expressions during food waste fermentation

Food waste(FW)has been recognized as essential reservoir for resource recovery via anaerobic fermentation,which could also bring the potential risk of antibiotic resistance genes(ARGs)dissemination.Although the structural deficiency of FW could be stimulated by enzymatic pretreatment to enhance fermentation efficiency,the influences of enzymatic pretreatment on ARGs fate and microbial metabolic pathways involved in ARGs dissemination have rarely been reported.This work proved that enzymatic pretreatment could effectively decrease the total abundance of ARGs(reduced by 13.8%-24.5%)during long-term FW fermentation.It was found that enzymatic pretreatment significantly reduced the ARGs belonging to the efflux pump,which might be ascribed to its ability to increase membrane permeability.Furthermore,enzymatic pretreatment was in favor of reducing microbial diversity and various potential ARGs host(e.g.,Methanosarcina,Clostridium,Prevotella,Parabacteroides).Also,this pretreatment remarkably up-regulated the genetic expressions involved in ABC transporter(e.g.,eryF and mntA)and down-regulated the genetic expressions that participated in DNA replication,two-component systems(e.g.,uphA and cckA),and quorum sensing(e.g.,rpfF and lsrG),thereby decreasing ARGs transmission.This study would expand the insight of the influences of pretreatment method on ARGs fate during FW fermentation,and offer practical guidance on the sustainable management of FW.

Co-fermentation of waste activated sludge with food waste for short-chain fatty acids production:effect of pH at ambient temperature

Effect of pH ranging from 4.0 to 11.0 on cofermentation of waste activated sludge(WAS)with food waste for short-chain fatty acids(SCFAs)production at ambient temperature was investigated in this study.Experimental results showed that the addition of food waste significantly improved the performance of WAS fermentation system,which resulted in the increases of SCFAs production and substrate reduction.The SCFAs production at pH 6.0,7.0,8.0,and 9.0 and fermentation time of 4 d was respectively 5022.7,6540.5,8236.6,and 7911.7 mg COD·L^(-1),whereas in the blank tests(no pH adjustment,pH 8.0(blank test 1),no food waste addition,pH 8.0(blank test 2),and no WAS addition(blank test 3))it was only 1006.9,971.1,and 1468.5 mg COD·L^(-1),respectively.The composition of SCFAs at pH from 6.0 to 9.0 was also different from other conditions and propionic acid was the most prevalent SCFA,which was followed by acetic and n-butyric acids,while acetic acid was the top product under other conditions.At pH 8.0 a higher volatile suspended solids(VSS)reduction of 16.6%for the mixture of WAS and food waste than the sole WAS indicated a synergistic effect existing in fermentation system with WAS and food waste.The influence of pH on the variations of nutrient content was also studied during anaerobic fermentation of the mixture of WAS and food waste at different pH conditions.The release of NH_(4)^(+)-N increased with fermentation time at all pH values investigated except 4.0,5.0 and in blank test one.The concentrations of soluble phosphorus at acidic pHs and in the blank test one were higher than those obtained at alkaline pHs.Ammonia and phosphorus need to be removed before the SCFAsenriched fermentation liquid from WAS and food waste was used as the carbon source.

Effect of the addition of organic carbon sources on nitrous oxide emission in anaerobic-aerobic(low dissolved oxygen)sequencing batch reactors

The effect of additional organic carbon sources on the production of nitrous oxide(N_(2)O)in anaerobicaerobic(low dissolved oxygen)real wastewater treatment system was investigated.In this paper,three laboratoryscale sequencing batch reactors(SBRs)(SBR-1,SBR-2 and SBR-3)were operating under an anaerobic-aerobic(low dissolved oxygen,0.15-0.45 mg·L^(-1))configuration.The SBRs were‘long-term cultured’respectively with a single municipal wastewater sample,sodium acetate,and a waste-activated sludge alkaline fermentation liquid as the additional carbon sources of real wastewater.Off-gas analysis showed that N_(2)O was emitted into the atmosphere during the aerobic(low dissolved oxygen)period in the three SBRs,and the order of N_(2)O emission rate was SBR-2>SBR-1>SBR-3.It was observed that the higher poly-β-hydroxyvalerate fraction of polyhydroxyalkanoates,the lower glycogen transformation and less nitrite accumulation was in SBR-3,while the opposite behavior was observed in SBR-2.Further research indicated that the interaction of the factors above potentially affected the N_(2)O emission in the anaerobic-aerobic(low dissolved oxygen)system.

Research on polyhydroxyalkanoates and glycogen transformations: Key aspects to biologic nitrogen and phosphorus removal in low dissolved oxygen systems

In this paper,a study was conducted on the effect of polyhydroxyalkanoates(PHA)and glycogen transformations on biologic nitrogen and phosphorus removal in low dissolved oxygen(DO)systems.Two laboratory-scale sequencing batch reactors(SBR1 and SBR2)were operating with anaerobic/aerobic(low DO,0.15-0.45 mg·L^(-1))configurations,which cultured a propionic to acetic acid ratio(molar carbon ratio)of 1.0 and 2.0,respectively.Fewer poly-3-hydroxybutyrate(PHB),total PHA,and glycogen transformations were observed with the increase of propionic/acetic acid,along with more poly-3-hydroxyvalerate(PHV)and poly-3-hydroxy-2-methyvalerate(PH2MV)shifts.The total nitrogen(TN)removal efficiency was 68%and 82%in SBR1 and SBR2,respectively.In the two SBRs,the soluble ortho-phosphate(SOP)removal efficiency was 94%and 99%,and the average sludge polyphosphate(poly-P)content(g·g-MLVSS^(-1))was 8.3%and 10.2%,respectively.Thus,the propionic to acetic acid ratio of the influent greatly influenced the PHA form and quantity,glycogen transformation,and poly-P contained in activated sludge and further determined TN and SOP removal efficiency.Moreover,significant correlations between the SOP removal rate and the(PHV+PH2MV)/PHA ratio were observed(R^(2)>0.99).Accordingly,PHA and glycogen transformations should be taken into account as key components for optimizing anaerobic/aerobic(low DO)biologic nitrogen and phosphorus removal systems.

A new process to improve short-chain fatty acids and bio-methane generation from waste activated sludge

As an important intermediate product, short-chain fatty acids（SCFAs） can be generated after hydrolysis and acidification from waste activated sludge, and then can be transformed to methane during anaerobic digestion process. In order to obtain more SCFA and methane,most studies in literatures were centered on enhancing the hydrolysis of sludge anaerobic digestion which was proved as un-efficient. Though the alkaline pretreatment in our previous study increased both the hydrolysis and acidification processes, it had a vast chemical cost which was considered uneconomical. In this paper, a low energy consumption pretreatment method, i.e. enhanced the whole three stages of the anaerobic fermentation processes at the same time, was reported, by which hydrolysis and acidification were both enhanced, and the SCFA and methane generation can be significantly improved with a small quantity of chemical input. Firstly, the effect of different pretreated temperatures and pretreatment time on sludge hydrolyzation was compared. It was found that sludge pretreated at 100°C for 60 min can achieve the maximal hydrolyzation. Further, effects of different initial p Hs on acidification of the thermal pretreated sludge were investigated and the highest SCFA was observed at initial p H 9.0with fermentation time of 6 d, the production of which was 348.63 mg COD/g VSS（6.8 times higher than the blank test） and the acetic acid was dominant acid. Then, the mechanisms for this new pretreatment significantly improving SCFA production were discussed. Finally,the effect of this low energy consumption pretreatment on methane generation was investigated.