Junqiu Wu

Fractions and biodegradability of dissolved organic matter derived from different composts

An experiment was conducted to determine the fractions of molecular weights (MW) and the biodegradability of dissolved organic matter (DOM) in mature composts derived from dairy cattle manure (DCM), kitchen waste (KW), cabbage waste (CW), tomato stem waste (TSW), municipal solid waste (MSW), green waste (GW), chicken manure (CM), sludge (S), and mushroom culture waste (MCW). There were distinct differences in the concentration and MW fractions of DOM, and the two measures were correlated. Fraction MW>5kDa was the major component of DOM in all mature composts. Determined 5day biochemical oxygen demand (BOD5) of DOM was correlated to the concentration of DOM and all MW fractions except MW>5kDa, indicating that the biodegradability of DOM was a function of the content and proportion of fraction MW<5kDa. This study suggests that the amount and distribution of low MW fractions affect DOM biodegradability.

Effect of precursors combined with bacteria communities on the formation of humic substances during different materials composting

The aim of this work was to put forward a method to improve HS amount by studying the formation regularity of HS. Five precursors have been detected and few researches combined them with bacteria to study HS formation. During composting, the polyphenols, carboxyl and amino acids concentration decreased by 75.8%, 63.2% and 68.3% on average, respectively. However, the polysaccharides, reducing sugars and HS concentration increased by 61.2%, 47.1% and 37.33% on average. Relationships between precursors and HS concentration showed that the HS formation were significantly affected (p<0.05). The key bacteria community and physical-chemical parameters which affected HS formation have also been identified by redundancy analysis. Twelve key bacteria communities have been selected, which were significantly affected by physical-chemical parameters (p<0.05). Accordingly, we proposed an adjusting method to promote HS amount during composting based on the relationship between the key bacteria communities and the precursors as well as physical-chemical parameters.

Identifying the key factors that affect the formation of humic substance during different materials composting

The aim of this work was to identify the factors which can affect humic substance (HS) formation. Composting periods, HS precursors, bacteria communities and environment factors were recognized as the key factors and few studies explored the potential relationships among them. During composting, HS precursors were mainly formed in the heating and thermophilic phases, but HS were polymerized in the cooling and mature phases. Moreover, bacterial species showed similar classification of community structure in the same composting period of different materials. Furthermore, structural equation model showed that NH4--N and NO3--N were the indirect environmental factors for regulating HS formation by the bacteria and precursors as the indirect and direct driver, respectively. Therefore, both environmental factors and HS precursors can be the regulating factors to promote HS formation. Given that, a new staging regulating method had been proposed to improve the amount of HS during different materials composting.

Snowmelt-driven changes in dissolved organic matter and bacterioplankton communities in the Heilongjiang watershed of China

Bacterioplankton plays a significant role in the circulation of materials and ecosystem function in the biosphere. Dissolved organic matter (DOM) from dead plant material and surface soil leaches into water bodies when snow melts. In our study, water samples from nine sampling sites along the Heilongjiang watershed were collected in February and June 2014 during which period snowmelt occurred. The goal of this study was to characterize changes in DOM and bacterioplankton community composition (BCC) associated with snowmelt, the effects of DOM, environmental and geographical factors on the distribution of BCC and interactions of aquatic bacterioplankton populations with different sources of DOM in the Heilongjiang watershed. BCC was measured by denaturing gradient gel electrophoresis (DGGE). DOM was measured by excitation-emission matrix (EEM) fluorescence spectroscopy. Bacterioplankton exhibited a distinct seasonal change in community composition due to snowmelt at all sampling points except for EG. Redundancy analysis (RDA) indicated that BCC was more closely related to DOM (Components 1 and 4, dissolved organic carbon, biochemical oxygen demand and chlorophyll a) and environmental factors (water temperature and nitrate nitrogen) than geographical factors. Furthermore, DOM had a greater impact on BCC than environmental factors (29.80 vs. 15.90% of the variation). Overall, spring snowmelt played an important role in altering the quality and quantity of DOM and BCC in the Heilongjiang watershed.

Effect of tricarboxylic acid cycle regulator on carbon retention and organic component transformation during food waste composting

Composting is an environment friendly method to recycling organic waste. However, with the increasing concern about greenhouse gases generated in global atmosphere, it is significant to reduce the emission of carbon dioxide (CO2). This study analyzes tricarboxylic acid (TCA) cycle regulators on the effect of reducing CO2 emission, and the relationship among organic component (OC) degradation and transformation and microorganism during composting. The results showed that adding adenosine tri-phosphate (ATP) and nicotinamide adenine dinucleotide (NADH) could enhance the transformation of OC and increase the diversity of microorganism community. Malonic acid (MA) as a competitive inhibitor could decrease the emission of CO2 by inhibiting the TCA cycle. A structural equation model was established to explore effects of different OC and microorganism on humic acid (HA) concentration during composting. Furthermore, added MA provided an environmental benefit in reducing the greenhouse gas emission for manufacture sustainable products.

Effect of cold-adapted microbial agent inoculation on enzyme activities during composting start-up at low temperature

In order to put forward a method to promote composting start-up at low ambient temperature, the cold-adapted microbial agent (CAMA) was inoculated in chicken manure (CM), and compared the enzymes activities, including urease, proteases, β-glucosidase and invertase, with no CAMA group (CK). In this study, the temperature of CM reached 50°C in 53h, but it in CK was only around 30°C during the composting process. Moreover, the enzymes exhibited higher activity in CM than CK, indicating the effectiveness of CAMA. Furthermore, redundancy analysis was conducted to study the relationships of CAMA, with enzymes activities and temperature. Results showed that the positive effect of CAMA on the enzyme activities were achieved by affecting the bacterial community structure. Accordingly, we provide a method to guide CAMA inoculation for promoting compost start-up in cold area.

Response of humic acid formation to elevated nitrate during chicken manure composting

Nitrate can stimulate microbes to degrade aromatic compounds, whereas humic acid (HA) as a high molecular weight aromatic compound, its formation may be affected by elevated nitrate during composting. Therefore, this study is conducted to determine the effect of elevated nitrate on HA formation. Five tests were executed by adding different nitrate concentrations to chicken manure composting. Results demonstrate that the concentration of HA in treatment group is significantly decreased compared with control group (p < 0.05), especially in the highest nitrate concentration group. RDA indicates that the microbes associated with HA and environmental parameters are influenced by elevated nitrate. Furthermore, structural equation model reveals that elevated nitrate reduces HA formation by mediating microbes directly, or by affecting ammonia and pH as the indirect drivers to regulate microbial community structure.

Improved lignocellulose-degrading performance during straw composting from diverse sources with actinomycetes inoculation by regulating the key enzyme activities

This study was conducted to assess the effect of thermophilic actinomycetes inoculation on the lignocellulose degradation, enzyme activities and microbial community during different types of straw composting from wheat, rice, corn and soybean. The results showed that actinomycetes inoculation not only changed the structure of actinomycetic and bacterial community but also accelerated the degradation of cellulose, hemicellulose and lignin and increased the key enzymes activities including CMCase, Xylanase, manganese peroxidase, lignin peroxidase and laccase during composting particularly from wheat straw and rice straw. The key enzyme and physiochemical parameters which affected organic fractions degradation have been identified by redundancy analysis. The combined application of actinomycete inoculation and urea addition as a source of nitrogen was suggested to regulate the key enzyme activities and lignocellulose degradation, which lays a foundation for effectively managing organic wastes from different types of crop straws by composting.

Effect of the addition of exogenous precursors on humic substance formation during composting

The aim of this work was to explore the effect of the addition of exogenous precursors on humic substance (HS) formation during composting. HS formation is a complex biochemical process that occurs during composting. In addition, HS precursors and bacterial communities were recognized as the key factors that affect HS formation. The addition of exogenous precursors can promote the humification process during composting, but few studies have explored the potential relationships between the proportion of additional exogenous precursors, the bacterial community and HS formation. Jointly adding benzoic acid (BA) and soybean residue after extracted oil (SR) treatment can promote HS formation, especially humic acid formation. In addition, the increase in the proportion of exogenous precursors added could strengthen the relationship among different precursors, thereby changing the bacterial community composition and further promoting the humification process during composting. In addition, a structural equation model (SEM) showed that precursors were the key factors to regulate HS formation and certain bacteria as the direct drivers to affect HS formation. This model provides more possibilities to regulate HS formation during composting and enhances its potential applicability under real conditions.

How does manganese dioxide affect humus formation during bio-composting of chicken manure and corn straw?

The aim of this study is to reveal the roles of MnO2 in Maillard reaction of biotic composting, and to identify its effectiveness in promoting humus formation. Corn straw (CS) and chicken manure (CM) have been chosen to be composted. During CS composting, addition of MnO2 rapidly reduced reducing sugars concentration (decreased by 84.0%) in 5 days and significantly improved humus production by 38.7% compared with treatment without MnO2. Whereas in CM composting, the promoting effect of MnO2 on humus formation was relatively weak by comparing with the treatment group of CS. Additionally, the presence of MnO2 has reshaped bacteria community, which might be the reason of MnO2 stimulated bacteria to utilize organic matter during CM composting. Therefore, the structural equation modeling has confirmed that MnO2 mainly performed as chemical catalyst to promote humus formation during CS composting. Besides catalyst, MnO2 also played as a bioactive activator in CM composting.