P. J. He

Impact of recycled effluent on the hydrolysis during anaerobic digestion of vegetable and flower waste

Two trials were established to investigate the effect of recycled effluent on hydrolysis during anaerobic co-digestion of vegetable and flower waste. Trial I evaluated the effect by regulating the flow rate of recycled effluent, while Trial II regulated the ratio of hydrolytic effluent to methanogenic effluent, which were recycled to hydrolysis reactor. Results showed that the recirculation of methanogenic effluent could enhance the buffer capability and operation stability of hydrolysis reactor. Higher recycled flow rate was favourable for microbial anabolism and further promoted hydrolysis. After 9 days of hydrolysis, the cumulative SCOD in the hydrolytic effluent reached 334, 407, 413, 581 mg/g at recycled flow rates of 0.1, 0.5, 1.0, 2.0 m3/(m3 x d), respectively. It was feasible to recycling a mixture of hydrolytic and methanogenic effluent to the hydrolysis reactor. This research showed that partially introducing hydrolytic effluent into the recycled liquid could enhance hydrolysis, while excessive recirculation of hydrolytic effluent will inhibit the hydrolysis. The flow ratio 1:3 of hydrolytic to methanogenic effluent was found to provide the highest hydrolysis efficiency and degradation rate of lignocelluloses-type biomass, among four ratios of 0:1, 1:3, 1:1 and 3:1. Under this regime, after 9 days of hydrolysis, the cumulative TOC and TN in the hydrolytic effluent reached 162 mg/g and 15 mg/g, the removal efficiency of TS, VS, C and cellulose in the solid phase were 60.66%, 62.88%, 58.35% and 49.12%, respectively. The flow ratio affected fermentation pathways, i.e. lower ratio favoured propionic acid fermentation and the generation of lactic acid while higher ratio promoted butyric acid fermentation.

Synergetic effect of pH and biochemical components on bacterial diversity during mesophilic anaerobic fermentation of biomass-origin waste

Aims:  To investigate the synergetic effect of pH and biochemical components on bacterial community structure during mesophilic anaerobic degradation of solid wastes with different origins, and under acidic or neutral conditions.

Effect of alkali metal cation on the anaerobic hydrolysis and acidogenesis of vegetable waste

Five batch testing scenarios were designed to evaluate the effects of alkali metal cations on anaerobic hydrolysis and acidogenesis. These scenarios were A (c=0 g l−1), B (cNa+ =25 g l−1), C (cNa+ =50 g l−1), D (cK+ =25 g l−1), and E (cK+ =50 g l−1, pH 7.0). A solution pH of 7.0 or above favored protein hydrolysis, higher proteinase activity and higher ammonia production. However, such a pH suppressed carbohydrate hydrolysis, as indicated by low α-amylase activity. Cation interference at pH 5.0–6.0 seemed not to affect carbohydrate hydrolysis, as showed by the unimpaired α-amylase activity at 50 g l−1 K+. Acidogenesis was more sensitive to alkali metal cations, so acid production and the drop in pH were lowest in a 25–50 g l−1 Na+, acidic environment (pH 4.0–6.0). It was insensitive to cations when the pH was maintained at 7.0–8.0. When the pH was uncontrolled and decreased freely to acidic values, 25 g l&minus1 of cation inhibited the action of the microbes, which rapidly acclimated, as presented by the slow transformation of soluble polymers to soluble metabolites. However, acidogenetic microbes could not easily recover from inhibition by 50 g l−1 of cation. When the pH was maintained at over 7.0, the microbes were not inhibited by cation (50 g l−1) as indicated by the more active acidogenesis. The metabolic pathways to lactate, acetate and alcohols were not fully coupled.

PARTITION OF SIX PHTHALIC ACID ESTERS IN SOLUBLE AND SOLID RESIDUAL FRACTIONS OF WASTEWATER SLUDGES

Abstract Distributions of six priority controlled Phthalic acid esters (PAEs), including di‐methyl phthalate (DMP), di‐ethyl phthalate (DEP), di‐butyl phthalate (DBP), benzyl butyl phthalate (BBP), di‐(2‐ethylhexyl) phthalate (DEHP), di‐octyl phthalate (DOP) were studied based on soluble and insoluble fractions of sludge samples collected at four wastewater treatment plants in Shanghai, China. Three sludge samples comprised hydrophilic colloidal particles of high protein contents and low aromaticity. Meanwhile, these sludges contained DBP of 4.2∼5.7 mg kg−1 dried solids (ds) and DEHP of 21.1∼55.6 mg kg−1 ds, respectively. Another sludge sample comprised mainly hydrophobic colloidal particles of humic substances and high aromaticity. It contained DBP of 1.18 mg kg−1 ds and DEHP of 2.89 mg kg−1 ds, respectively. The most abundant components noted amongst the six studied PAEs were DBP and DEHP, which mostly associated with the insoluble fraction of sludge. Specifically, the DBP and DEHP in insoluble fraction (the solid residual phase) accounted for 89.8∼98.2% and 88.6∼99.6% of those in the whole sludge. The partition coefficients of DBP and DEHP for the soluble and insoluble fractions of sludge correlated with the suspension SUVA254, suggesting that interaction between π‐electrons of DBP or DEHP and those of organic particulates in suspension contributes most of the sorption processes.

Effect of ammonia on methane production pathways and reaction rates in acetate-fed biogas processes

In order to understand the correlation between ammonia and methanogenesis metabolism, methane production pathways and their specific rates were studied at total ammonium nitrogen (TAN) concentrations of 0.14-9 g/L in three methanogenic sludges fed with acetate, at both mesophilic and thermophilic conditions. Results showed that high levels of TAN had significant inhibition on methanogenesis; this could, however, be recovered via syntrophic acetate oxidation (SAO) coupled with Hydrogenotrophic Methanogenesis (HM) performed by acetate oxidizing syntrophs or through Acetoclastic Methanogenesis (AM) catalyzed by Methanosarcinaceae, after a long lag phase >50 d. Free ammonia (NH3) was the active component for this inhibition, of which 200 mg/L is suggested as the threshold for the pathway shift from AM to SAO-HM. Methane production rate via SAO-HM at TAN of 7-9 g/L was about 5-9-fold lower than that of AM at TAN of 0.14 g/L, which was also lower than the rate of AM pathway recovered at TAN of 7 g/L in the incubations with a French mesophilic inoculum. Thermophilic condition favored the establishment of the SAO-catalyzing microbial community, as indicated by the higher reaction rate and shorter lag phase. The operational strategy is thus suggested to be adjusted when NH3 exceeds 200 mg/L.

Comparison of different fluorescence spectrum analysis techniques to characterize humification levels of waste-derived dissolved organic matter

In the present work, the humification level of waste-derived dissolved organic matter (DOM) at different waste biostability was investigated, by using fluorescent excitation-emission matrix (EEM) scanning. Different fluorescence spectrum analysis techniques were applied and compared. Experimental results demonstrate that parallel factor (PARAFAC) analysis was sensitive to reflect DOM humification, and the most reasonable to deconstruct DOM compositions, when compared with other spectrum analysis techniques. It suggests applying the DOM–EEM–PARAFAC pipeline for rapid estimation of waste biostability.

Similar evolution in δ 13CH4 and model-predicted relative rate of aceticlastic methanogenesis during mesophilic methanization of municipal solid wastes

Similar evolution was obtained for the stable carbon isotope signatures delta (13)CH(4) and the model-predicted relative rate of aceticlastic methanogenesis during mesophilic methanization of municipal solid wastes. In batch incubations, the importance of aceticlastic and hydrogenotrophic methanogenesis changes in time. Initially, hydrogenotrophic methanogenesis dominated, but increasing population of Methanosarcina sp. enhances aceticlastic methanogenesis. Later, hydrogenotrophic methanogenesis intensified again. A mathematical model was developed to evaluate the relative contribution of hydrogenotrophic and aceticlastic pathways of methane generation during mesophilic batch anaerobic biodegradation of the French and the Chinese Municipal Solid Wastes (FMSW and CMSW). Taking into account molecular biology analysis reported earlier three groups of methanogens including strictly hydrogenotrophic methanogens, strictly aceticlastic methanogens (Methanosaeta sp.) and Methanosarcina sp., consuming both acetate and H(2)/H(2)CO(3) were considered in the model. The total organic and inorganic carbon concentrations, methane production volume, methane and carbon dioxide partial pressures values were used for the model calibration and validation. Methane isotopic composition (delta (13)CH(4)) evolution during the incubations was used to independently validate the model results. The model demonstrated that only the putrescible solid waste was totally converted to methane.

Nitrogen removal from landfill leachate using single or combined processes.

The municipal solids waste (MSW) collected at Shanghai includes a high proportion of food waste, which is easily hydrolyzed to generate ammonia-nitrogen in leachate. This study investigated the efficiency of nitrogen removal from landfill leachate employing four different treatment processes. The simulated rainfall and direct leachate recycling produced strong leachate with high ammonia-nitrogen content, and resulted in the removal of only a small amount of nitrogen. Although pretreating the leachate using an aerobic reactor removed some nitrogen, most of which was transformed to biomass because of the high organic loading applied. Using the three-compartment system, which comprises a landfill column with fresh MSW, a column with well-decomposed refuse layer as the methane generator, and a nitrifier, the ammonia-nitrogen was converted into nitrogen gas and hence removed. Experimental results demonstrated the feasibility of adopting the three-compartment system for managing nitrogen in landfill leachate generated from high-nitrogen-content MSW.

Clean-up and disposal process of polluted sediments from urban rivers

In this paper, the discussion is concentrated on the properties of the polluted sediments and the combination of clean-up and disposal process for the upper layer heavily polluted sediments with good flowability. Based on the systematic analyses of various clean-up processes, a suitable engineering process has been evaluated and recommended. The process has been applied to the river reclamation in Yangpu District of Shanghai City, China. An improved centrifuge is used for dewatering the dredged sludge, which plays an important role in the combination of clean-up and disposal process. The assessment of the engineering process shows its environmental and technical economy feasibility, which is much better than that of traditional dredging-disposal processes.

Removing Particulates from Centrate of Dredged Sediments at Suitanghe River, Shanghai

The centrifugal dewatering of dredged slurry from a contaminated river would produce centrate that contained high levels of pollutants and particulates. The direct discharge of the centrate back to the river has predominant negative effects on the river water quality. In this study, particulates in the centrate were proposed to be removed by the use of a combined clarification+sand filtration+ultra filtration process. Jar tests revealed that dual conditioning by 100 mg/L polyaluminum chloride (PACl) followed by 30 mg/L polyacrylamide (PAM) obtained a more satisfactory effluent quality than single coagulant conditioning. Process parameters for clarification stage were then optimized using orthogonal tests at bench-scale tester. The helical-flow contact clarification could effectively remove particulate matters from the centrate with a hydraulic retention time (HRT) of 25 min. Since most pollutants were strongly associated with the particulates, the removal of suspended solids could effectively decontaminate the discharge as well. The effluent quality from sand filter could meet with the Class II criteria of Integrated Wastewater Discharge Standard in China (GB8978-1996, Integrated Wastewater Discharge Standard (in Chinese); National Environmental Protection Agency of China: Beijing, China, 1996), whereas that from ultrafilter met with the Water Quality Standard for Non-potable Use of China (CJ25.1–89, Water Quality for Non-protable Use (in Chinese); Construction Ministry of China: Beijing, China, 1989).