Jibao Liu

Optimization and microbial community analysis of anaerobic co-digestion of food waste and sewage sludge based on microwave pretreatment

The effects of microwave pretreatment (MW) on co-digestion of food waste (FW) and sewage sludge (SS) have never been investigated. In this study, a series of mesophilic biochemical methane potential (BMP) tests were conducted to determine the optimized ratio of FW and SS based on MW, and the evolution of bacterial and archaeal community was investigated through high-throughput sequencing method. Results showed that the optimized ratio was 3:2 for co-digestion of FW and SS based on MW, and the methane production was 316.24 and 338.44mLCH4/gVSadded for MW-FW and MW-SS, respectively. The MW-SS was superior for methane production compared to MW-FW, in which accumulation of propionic acid led to the inhibition of methanogenesis. Proteiniborus and Parabacteroides were responsible for proteins and polysaccharides degradation for all, respectively, while Bacteroides only dominated in co-digestion. Methanosphaera dominated in MW-FW at the active methane production phase, while it was Methanosarcina in MW-SS and mono-SS.

Microwave-acid pretreatment: A potential process for enhancing sludge dewaterability.

Activated sludge is hard to be dewatered due to the highly water bounded in sludge flocs. This study investigated the hybrid treatment of microwave irradiation and acidification on sludge dewaterability as well as its mechanism. Results showed that the combined microwave-acid treatment (Txa0=xa0100xa0°C, initial pHxa0=xa02.5) was effective for improving sludge dewaterability, e.g. capillary suction time (CST) decreased from 37.7xa0s to 9.2xa0s, bound water content decreased from 1.96xa0±xa00.19xa0g/g Dry Sludge (DS) to 0.88xa0±xa00.24xa0g/g DS. The treated sludge showed more fluidity and less thixotropy. Both MW heating temperature and pH played important roles in improving sludge dewaterability. Higher temperature was beneficial for sludge disintegration, but the released polymers resulted in highly negative zeta potential and deteriorated sludge dewaterability. The acidification was capable of reducing the negative zeta potential, increasing flocs size and finally improving sludge dewaterability. According to the analysis of molecule weight distribution and 3D-EEM, the fractions of polymers especially protein-like substances at molecule weight of 10(4)-10(5)xa0Da were the key organics related to sludge dewaterability, but not the humic acid-like and fulvic acid-like substances.

Rheological properties of sewage sludge during enhanced anaerobic digestion with microwave-H2O2 pretreatment

The rheological behavior of sludge is of serious concern in anaerobic digestion. This study investigated the rheological properties of sewage sludge during enhanced anaerobic digestion with microwave-H2O2 pretreatment (MW-H2O2). The results showed that MW-H2O2 pretreatment resulted in the improvement of sludge flowability and weakening of its viscoelastic properties. Further positive effects on the rheological properties of digested sludge during anaerobic digestion were observed. The flowability was improved with a low level of apparent viscosity. The decrease of the consistency index and increase of the flow behavior index indicated that the strength of the inner structures and non-Newtonian flow characteristics of digested sludge weakened. Both the storage modulus (G) and loss modulus (G″) decreased, indicating that the viscoelastic behavior became weak. These effects were possibly attributed to the changes of the digested sludge micro-structures, such as extracellular polymeric substances (EPS). This study concluded that anaerobic digestion for treating sewage sludge combined with pretreatment is a more favorable option than single anaerobic digestion from the perspective of rheology.

Biogas-pH automation control strategy for optimizing organic loading rate of anaerobic membrane bioreactor treating high COD wastewater.

Control of organic loading rate (OLR) is essential for anaerobic digestion treating high COD wastewater, which would cause operation failure by overload or less efficiency by underload. A novel biogas-pH automation control strategy using the combined gas-liquor phase monitoring was developed for an anaerobic membrane bioreactor (AnMBR) treating high COD (27.53 g·L(-1)) starch wastewater. The biogas-pH strategy was proceeded with threshold between biogas production rate >98 Nml·h(-1) preventing overload and pH>7.4 preventing underload, which were determined by methane production kinetics and pH titration of methanogenesis slurry, respectively. The OLR and the effluent COD were doubled as 11.81 kgCOD·kgVSS(-1)·d(-1) and halved as 253.4 mg·L(-1), respectively, comparing with a constant OLR control strategy. Meanwhile COD removal rate, biogas yield and methane concentration were synchronously improved to 99.1%, 312 Nml·gCODin(-1) and 74%, respectively. Using the biogas-pH strategy, AnMBR formed a pH self-regulation ternary buffer system which seizes carbon dioxide and hence provides sufficient buffering capacity.

Pilot-scale study of sludge pretreatment by microwave and sludge reduction based on lysis-cryptic growth

To evaluate the performance of microwave (MW)-chemical hybrid sludge treatment system, a pilot scale MW disintegration unit (treatment capacity of 500L/d) was constructed. The results showed that organic matter, nitrogen, and phosphorus were effectively released from the MW-pretreated sludge. The values of COD released were 15.91%, 15.07%, 13.83%, 19.35%, and 15.07% for the MW, MW-acid, MW-alkali, MW-H2O2, and MW-H2O2-alkali treatment processes, respectively. Additionally, for a wastewater treatment system with a capacity of 200m(3)/d, when coupled with a MW sludge pretreatment unit, the sludge production and sludge yield were greatly reduced by 38.60% and to 0.35kg VSS/kg CODconsumed, respectively. The total operating cost of the lysis-cryptic growth system was 13.64% lower than that of the CAS system without a MW unit.

Fate of antibiotic resistance bacteria and genes during enhanced anaerobic digestion of sewage sludge by microwave pretreatment

The fate of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) were investigated during the sludge anaerobic digestion (AD) with microwave-acid (MW-H), microwave (MW) and microwave-H2O2-alkaline (MW-H2O2) pretreatments. Results showed that combined MW pretreatment especially for the MW-H pretreatment could efficiently reduce the ARB concentration, and most ARG concentrations tended to attenuate during the pretreatment. The subsequent AD showed evident removal of the ARB, but most ARGs were enriched after AD. Only the concentration of tetX kept continuous declination during the whole sludge treatment. The total ARGs concentration showed significant correlation with 16S rRNA during the pretreatment and AD. Compared with unpretreated sludge, the AD of MW and MW-H2O2 pretreated sludge presented slightly better ARB and ARGs reduction efficiency.

Advanced treatment of municipal wastewater by nanofiltration： Operational optimization and membrane fouling analysis

Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration (NF) in this study. The NF performance was optimized, and its fouling characteristics after different operational durations (i.e., 48 and 169hr) were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure=12bar, pH=4 and flow rate=8L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6hr which is 175% longer than that of the 48-hr one. High molecular weight (MW) protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.

CFD simulation and optimization of membrane scouring and nitrogen removal for an airlift external circulation membrane bioreactor

Cost-effective membrane fouling control and nitrogen removal performance are of great concern in airlift external circulation membrane bioreactors (AEC-MBRs). Computational fluid dynamics (CFD) model incorporating sub-models of bio-kinetics, oxygen transfer and sludge rheology was developed for the cost-effective optimization of a lab-scale AEC-MBR. The model was calibrated and validated by extensive measurements of water velocities and water quality parameters in the AEC-MBR. The validated results demonstrated that the optimized height of gas-liquid dispersion was at around 300mm. The shear stress on membrane surface was equalized and had an average value of 1.2Pa under an air flowrate of 1.0m(3)h(-1). The model further revealed that the high nitrogen removal efficiency (>90%) was achieved due to the high recirculation ratio driven by airlift force without destroying the oxygen deprivation and enrichment in the anoxic and oxic zone, respectively.

Does residual H2O2 result in inhibitory effect on enhanced anaerobic digestion of sludge pretreated by microwave-H2O2 pretreatment process?

This study investigated the effects of residual H2O2 on hydrolysis-acidification and methanogenesis stages of anaerobic digestion after microwave-H2O2 (MW-H2O2) pretreatment of waste activated sludge (WAS). Results showed that high sludge solubilization at 35–45xa0% was achieved after pretreatment, while large amounts of residual H2O2 remained and refractory compounds were thus generated with high dosage of H2O2 (0.6xa0g H2O2/g total solids (TS), 1.0xa0g H2O2/g TS) pretreatment. The residual H2O2 not only inhibited hydrolysis-acidification stage mildly, such as hydrolase activity, but also had acute toxic effect on methanogens, resulting in long lag phase, low methane yield rate, and no increase of cumulative methane production during the 30-day BMP tests. When the low dosage of H2O2 at 0.2xa0g H2O2/g TS was used in MW-H2O2 pretreatment, sludge anaerobic digestion was significantly enhanced. The cumulative methane production increased by 29.02xa0%, but still with a lag phase of 1.0xa0day. With removing the residual H2O2 by catalase, the initial lag phase of hydrolysis-acidification stage decreased from 1.0 to 0.5xa0day.

A comprehensive insight into the effects of microwave-H2O2 pretreatment on concentrated sewage sludge anaerobic digestion based on semi-continuous operation

This study gave a comprehensive insight into the effects of microwave-H2O2 pretreatment on concentrated sludge anaerobic digestion (AD). Results showed that mixture of activated sludge and pretreated sludge at mass ratio of 1:1 was efficient for enhancing AD, methane production was increased from 215.51u202fmL/g VSadded to 258.38u202fmL/g VSadded. Pretreatment resulted in the change of sludge properties, such as solubilization of organic matters, decrease of viscosity. For concentrated sludge AD, the pH buffer system ensured the inhibitory steady state during start-up period, and significant archaeal community shift from Methanosaeta to Methanosarcina ensured the true steady-state operation. Pretreatment further increased the relative abundance of functional microbia such as Bacteroidales, Clostridiales and Methanosarcina, and resulted in the decrease of viscosity of digested sludge in reactors. Based on the CFD simulation, the flow velocity became greater than the control. These comprehensive effects might contribute to enhanced efficiency of concentrated sludge AD.