Chuandong Wu

New insights into the interactions between carbon dioxide and ammonia emissions during sewage sludge composting.

This study aimed to investigate the role of carbon dioxide in reducing ammonia emissions. Three variations of a composting experiment were conducted in a laboratory-scale reactor, all of which exhibited the three typical composting phases. Approximately 70% of the ammonia emissions occurred within 96-144 h of the thermophilic stage. The maximum rate of change for the carbon dioxide emissions occurred at different times for different carbon source types, mixing rates, and addition times. The rate of change and total concentration of emitted carbon dioxide played a crucial role in ammonia emission due to their relationship to the intensity of ammonia assimilation. The addition of a carbon source that could be utilized by thermophilic microorganisms stimulated ammonia assimilation and thus reduced ammonia emissions. These findings suggested that the addition of a 7:3 mixture of sucrose and straw powder at 108 h is suitable for reducing ammonia emissions.

Feasibility of co-composting of sewage sludge, spent mushroom substrate and wheat straw.

In this study, the lab-scale co-composting of sewage sludge (SS) with mushroom substrate (SMS) and wheat straw (WS) conducted for 20days was evaluated. The addition of SMS evidently increased CO2 production and dehydrogenase activity. The combined addition of SMS and WS significantly improved the compost quality in terms of temperature, organic matter degradation and germination index, especially, reduced 21.9% of NH3 emission. Thats because SMS and WS possessed the complementarity of free air space and contained plenty of degradable carbon source. The SMS could create a comfortable environment for the nitrifying bacteria and improve nitrification. The carbohydrates from combined addition of SMS and WS could be utilized by thermophilic microorganisms, stimulate ammonia assimilation and reduce NH3 emission. These results suggested that adding SMS and WS could not only improve the degradation of organic matter and the quality of compost product, but also stimulate ammonia assimilation and reduce ammonia emission.

Usage of pumice as bulking agent in sewage sludge composting.

In this study, the impacts of reused and sucrose-decorated pumice as bulking agents on the composting of sewage sludge were evaluated in the lab-scale reactor. The variations of temperature, pH, NH3 and CO2 emission rate, moisture content (MC), volatile solid, dissolved organic carbon, C/N and the water absorption characteristics of pumice were detected during the 25days composting. The MC of pumice achieved 65.23% of the 24h water absorptivity within the first 2h at the mass ratio of 0.6:1 (pumice:sewage sludge). Reused pumice increased 23.68% of CO2 production and reduced 21.25% of NH3 emission. The sucrose-decorated pumice reduced 43.37% of nitrogen loss. These results suggested that adding pumice and sucrose-decorated pumice in sludge composting matrix could not only adjust the MC of materials, but also improve the degradation of organic matters and reduce nitrogen loss.

Effects of sucrose amendment on ammonia assimilation during sewage sludge composting

The aim of this study was to evaluate the laboratory-scale composting of sewage sludge and pumice mixtures that were amended with sucrose. The variation in temperature, pH, NH4(+)-N, ammonia emission, bacterial community, ammonia assimilating bacteria (AAB) populations and enzymatic activity related to ammonia assimilation were detected. The addition of sucrose increased the AAB population by 2.5-3.5 times, reduced ammonia emission by 24.7-31.1% compared with the control treatment, and promoted the growth of Bacillus and Wautersiella. The activities of glutamate dehydrogenase (GDH), glutamate synthase (GS) and glutamine synthetase (GOGAT), were enhanced by the addition of sucrose. GDH made a substantial contribution to ammonia assimilation when the ammonia concentration was high (⩾1.5g/kg) in the thermophilic phase. The GS/GOGAT cycle played an important role at low ammonia concentrations (⩽1.1g/kg) in the cooling phase. These results suggested that adding sucrose to sludge compost could promote ammonia assimilation and reduce ammonia emission.

Microbial community composition and function in a pilot-scale anaerobic-anoxic-aerobic combined process for the treatment of traditional Chinese medicine wastewater

Biodegradation of traditional Chinese medicine (TCM) wastewater was investigated in a pilot-scale anaerobic-anoxic-aerobic combined process, which was composed of an expanded granular sludge blanket (EGSB) reactor, a hydrolysis acidification (HA) reactor and a biological contact oxidation (BCO) reactor. In stable stage, the average values of COD and color in the combined process effluent were 45.7mgL-1 and 13 times, respectively. Excellent linear relations (R2>0.915) were achieved between color and UV254 at three color levels. Comprehensive community structures of the combined process were analysed by Illumina MiSeq Sequencing, which revealed that microbial community in the aerobic reactor had the greatest diversity and richness. Bacteroidetes, Firmicutes and Proteobacteria were dominant phyla in the three reactors, and Bacteroidales, Geobacter, ZB2 were the predominant functional microorganisms in the anaerobic, anoxic and aerobic reactors, respectively. Good removal efficiencies and presence of core microorganisms confirmed that the combined process was feasible for treating TCM wastewater.

Improving sewage sludge composting by addition of spent mushroom substrate and sucrose

The effects of spent mushroom substrate (SMS) and sucrose (S) amendment on emissions of nitrogenous gas (mainly NH3 and N2O) and end products quality of sewage sludge (SS) composting were evaluated. Five treatments were composted for 20 days in laboratory-scale using SS with different dosages of SMS and S, without additive amended treatment used as control. The results indicated that SMS amendments especially combination with S promoted dehydrogenase activity, CO2 production, organic matter degradation and humification in the composting, and maturity indices of composting also showed that the 30%SMS+2%S treatment could be much more appropriate to improve the composting process, such as total Kjeldahl nitrogen, nitrification index, humic acids/fulvic acids ratio and germination index, while the emissions of NH3 and N2O were reduced by 34.1% and 86.2%, respectively. These results shown that the moderate addition of SMS and S could improve the compost maturity and reduce nitrogenous gas emission.

Insight into effects of mature compost recycling on N 2 O emission and denitrification genes in sludge composting

Mature compost recycling is widely used to reduce the dosage of organic bulking agent in actual composting process. In this study, the effects of mature compost amendment on N2O emission and denitrification genes were investigated in 47 days composting of sewage sludge and rice husks. The results showed that mature compost amendment dramatically augmented N2O emission rate in mesophilic phase and CO2 emission rate in thermophilic phase of composting, respectively. The cumulative amount of N2O emission increased by more than 23 times compared to the control. Mature compost amendment not only reduced moisture and pH, but also significantly increased NO3--N and NO2--N concentrations. The correlation matrices indicated that NO3--N, narG and norB were the main factors influencing N2O emission rate in sludge composting with mature compost recycling, but the N2O emission rate was significantly correlated to NO2--N, nirK and norB in the control.

Characterizing the distribution of organic matter during composting of sewage sludge using a chemical and spectroscopic approach

The present study aimed to investigate the evolution of organic matters during sewage sludge composting with different carbon additives including glucose, sucrose and straw. The organic matters were divided into a hot water soluble fraction (SOL-H2O), neutral detergent soluble fraction (SOL-ND), hemicellulose-like fraction (HEM), cellulose-like fraction (CEL) and lignin-like fraction (LIG) by a modified Van Soest procedure. Parallel factor (PARAFAC) analysis was applied to identify the number of fluorescent components in excitation–emission matrixes (EEMs) and its relative concentration in each water extractable organic matter (WEOM) sample. The results showed that the degradation of total organic carbon (TOC) in SOL-H2O and SOL-ND, as well as HEM and CEL fractions was accelerated by adding glucose and sucrose. While the straw powder increased the amount of TOC in the HEM and CEL fractions, no promotion on the degradation of TOC was observed. Four components including humic-like, tryptophan-like, microbial byproduct-like and fulvic-like substances were identified by PARAFAC analysis of EEMs. The percentage of humic-like substances in the composted material increased from 42.7% to 51.6% due to the addition of sucrose. The results suggested that adding glucose and sucrose in sewage sludge composting could promote the degradation and humification of organic matters.