•Appropriate precursor concentration for magnetic biochar led to the improvement of methane production.•Microorganisms participating in anaerobic digestion were enriched on magnetic biochar.•Magnetic biochar offers a solution for preventing methanogens loss in anaerobic digesters.Magnetic biochar is a potential economical anaerobic digestion (AD) additive. To better understand the possible role of magnetic biochar for the improvement of biomethanization performance and the retention of methanogens, magnetic biochar fabricated under different precursor concentrations were introduced into organic fraction of municipal solid waste (OFMSW) slurry AD system. Results showed that methane production in AD treatment with magnetic biochar fabricated under 3.2 g FeCl3:100 g rice-straw ratio increased by 11.69% compared with control treatment without biochar addition, due to selective enrichment of microorganisms participating in anaerobic digestion on magnetic biochar. AD treatment with magnetic biochar fabricated under 32 g FeCl3:100 g rice-straw ratio resulted in 38.34% decreasement of methane production because of the competition of iron oxide for electron. Furthermore, 25% of total methanogens were absorbed on magnetic biochar and can be harvested with magnet, which can offer a potential solution for preventing the methanogens loss in the anaerobic digesters.

Recalcitrant charcoal application is predicted to decelerate global warming through creating a long-term carbon sink in soil. Although many studies have showed high stability of charcoal derived from woody materials, few have focused on the dynamics of straw-derived charcoal in natural environment on a long timescale to evaluate its potential for agricultural carbon sequestration. Here, we examined straw-derived charcoal in an ancient paddy soil dated from ~3700 calendar year before present (cal. year bp). Analytical results showed that soil organic matter consisted of more than 25 % of charcoal in charcoal-rich layer. Similarities in morphology and molecular structure between the ancient and the fresh rice-straw-derived charcoal indicated that ancient charcoal was derived from rice straw. The lower carbon content, higher oxygen content, and obvious carbonyl of the ancient charcoal compared with fresh rice straw charcoal implied that oxidation occurred in the scale of thousands years. However, the dominant aromatic C of ancient charcoal indicated that rice-straw-derived charcoal was highly stable in the buried paddy soil due to its intrinsic chemical structures and the physical protection of ancient paddy wetland. Therefore, it may suggest that straw charcoal application is a potential pathway for C sequestration considering its longevity.

Overuse of chemical fertilizer in agriculture has caused serious nitrogen (N) loss and water pollution problems in China. Biochar has the potential ability to reduce N loss and increase crop yield. However, there is still limited knowledge of the impacts of different biochars on N loss and crop yield over agriculturally relevant time frames. In this study, we compared the effects of amendment with bamboo biochar and rice straw biochar on the N retention and rice productivity in paddy fields, over an agriculturally relevant time span of 2 years.A 2-year field study was conducted to investigate the effects of bamboo biochar and rice straw biochar amendment at a rate of 22.5 t ha−1 (with or without urea) on N retention and rice growth. Total nitrogen (TN), ammonia (NH4+-N), and nitrate (NO3−-N) in soil and surface water were determined after biochar application. Stem lengths and rice yield were monitored during the experiment.Amendment with rice straw biochar resulted in higher rice yields than in paddy soils that had bamboo biochar amendments. Incorporating rice straw biochar into a paddy field increased the rice yield by 19.8 % in 2009 and 21.6 % in 2010 without urea (P < 0.05) and by 11.3 % in 2009 (P < 0.05) and 14.4 % in 2010 with urea, compared with their corresponding control treatments. Although there were no significant impacts on the surface water N runoff potential, biochar amendment did result in a significant increase in the NO3−-N content of rhizosphere soil—121.2–135.7 % with urea and 89.7–102.2 % without urea, respectively, at the tillering stage in the first year (P < 0.05).These results show that carbonizing rice straw residue into biochar and incorporating it into soil has the potential to enhance rice productivity and N retention in a paddy field.

Although nitrous oxide (N2O) emissions from composting contribute to the accelerated greenhouse effect, it is difficult to implement practical methods to mitigate these emissions. In this study, the effects of biochar amendment during pig manure composting were investigated to evaluate the inter-relationships between N2O emission and the abundance of denitrifying bacteria. Analytical results from two pilot composting treatments with (PWSB, pig manure + wood chips + sawdust + biochar) or without (PWS, pig manure + wood chips + sawdust) biochar (3% w/w) demonstrated that biochar amendment not only lowered NO2–-N concentrations but also lowered the total N2O emissions from pig manure composting, especially during the later stages. Quantification of functional genes involved in denitrification and Spearman rank correlations matrix revealed that the N2O emission rates correlated with the abundance of nosZ, nirK, and nirS genes. Biochar-amended pig manure had a higher pH and a lower moisture content. Biochar amendment altered the abundance of denitrifying bacteria significantly; less N2O-producing and more N2O-consuming bacteria were present in the PWSB, and this significantly lowered N2O emissions in the maturation phase. Together, the results demonstrate that biochar amendment could be a novel greenhouse gas mitigation strategy during pig manure composting.

Directly returning straw back to the paddy field would significantly accelerate methane (CH4) emission, although it may conserve and sustain soil productivity. The application of biochar (biomass-derived charcoal) in soil has been proposed as a sustainable technology to reduce methane (CH4) emission and increase crop yield. We compared the effects of either biochar or rice straw addition with a paddy field on CH4 emission and rice yield.A 2-year field experiment was conducted to investigate a single application of rice straw biochar (SC) and bamboo biochar (BC) (at 22.5 t ha−1) in paddy soil on CH4 emission and rice yield as compared with the successive application (6 t ha−1) of rice straw (RS). Soil chemical properties and methanogenic and CH4 oxidation activities in response to the amendment of biochar and rice straw were monitored to explain possible mechanism.SC was more efficient in reducing CH4 emission from paddy field than BC. Incorporating SC into paddy field could decrease CH4 emission during the rice growing cycle by 47.30 %–86.43 % compared with direct return of RS. This was well supported by the significant decrease of methanogenic activity in paddy field with SC. In comparison to a non-significant increase with BC or RS application, rice yield was significantly raised with SC amendment by 13.5 % in 2010 and 6.1 % in 2011. An enhancement of available K and P and an improvement in soil properties with SC amendment might be the main contributors to the increased crop yield.These results indicated that conversion of RS into biochar instead of directly returning it to the paddy field would be a promising method to reduce CH4 emission and increase rice yield.

In order to obtain insight into the prokaryotic diversity and community in leachate sediment, a culture-independent DNA-based molecular phylogenetic approach was performed with archaeal and bacterial 16S rRNA gene clone libraries derived from leachate sediment of an aged landfill. A total of 59 archaeal and 283 bacterial rDNA phylotypes were identified in 425 archaeal and 375 bacterial analyzed clones. All archaeal clones distributed within two archaeal phyla of the Euryarchaeota and Crenarchaeota, and well-defined methanogen lineages, especially Methanosaeta spp., are the most numerically dominant species of the archaeal community. Phylogenetic analysis of the bacterial library revealed a variety of pollutant-degrading and biotransforming microorganisms, including 18 distinct phyla. A substantial fraction of bacterial clones showed low levels of similarity with any previously documented sequences and thus might be taxonomically new. Chemical characteristics and phylogenetic inferences indicated that (1) ammonium-utilizing bacteria might form consortia to alleviate or avoid the negative influence of high ammonium concentration on other microorganisms, and (2) members of the Crenarchaeota found in the sediment might be involved in ammonium oxidation. This study is the first to report the composition of the microbial assemblages and phylogenetic characteristics of prokaryotic populations extant in leachate sediment. Additional work on microbial activity and contaminant biodegradation remains to be explored.

A potential means to diminish increasing levels of CO2 in the atmosphere is the use of pyrolysis to convert biomass into biochar, which stabilizes the carbon (C) that is then applied to soil. Before biochar can be used on a large scale, especially in agricultural soils, its effects on the soil system need to be assessed. This is especially important in rice paddy soils that release large amounts of greenhouse gases to the atmosphere.In this study, the effects of biochar on CH4 and CO2 emissions from paddy soil with and without rice straw added as an additional C source were investigated. The biochars tested were prepared from bamboo chips or rice straw which yielded bamboo char (BC) and straw char (SC), respectively. BC and SC were applied to paddy soil to achieve low, medium, and high rates, based on C contents of the biochars. The biochar-amended soils were incubated under waterlogged conditions in the laboratory.Adding rice straw significantly increased CH4 and CO2 emissions from the paddy soil. However, when soils were amended with biochar, CH4 emissions were reduced. CH4 emissions from the paddy soil amended with BC and SC at high rate were reduced by 51.1% and 91.2%, respectively, compared with those without biochar. Methanogenic activity in the paddy soil decreased with increasing rates of biochar, whereas no differences in denaturing gradient gel electrophoresis patterns were observed. CO2 emission from the waterlogged paddy soil was also reduced in the biochar treatments.Our results showed that SC was more effective than BC in reducing CH4 and CO2 emissions from paddy soils. The reduction of CH4 emissions from paddy soil with biochar amendment may result from the inhibition of methanogenic activity or a stimulation of methylotrophic activity during the incubation period.

Biochar can play a key role in nutrient cycling, potentially affecting nitrogen retention when applied to soils. In this project, laboratory experiments were conducted to investigate the adsorption properties of bamboo charcoal (BC) and the influence of BC on nitrogen retention at different soil depths using multi-layered soil columns. Results showed that BC could adsorb ammonium ion predominantly by cation exchange. Ammonium nitrogen (NH4+-N) concentrations in the leachate of the soil columns showed significant differences at different depths after ammonium chloride application to the columns depending on whether BC had been added. Addition of 0.5% BC to the surface soil layer retarded the downward transport of NH4+-N in the 70-day experiment, as indicated by measurements made during the first 7 days at 10 cm, and later, in the experimental period at 20 cm. In addition, application of BC reduced overall cumulative losses of NH4+-N via leaching at 20 cm by 15.2%. Data appeared to suggest that BC could be used as a potential nutrient-retaining additive in order to increase the utilization efficiency of chemical fertilizers. Nonetheless, the effect of BC addition on controlling soil nitrogen losses through leaching needs to be further assessed before large-scale applications to agricultural fields are implemented.

Genetic modifications (GM) of commercial crops offer many benefits. However, microbial-mediated decomposition might be affected by GM crop residues in agricultural ecosystems. The objective of this study was to assess the possible impacts of cry1Ab gene transformation of rice on soil microbial community composition associated with residue decomposition in the paddy field under intensive rice cultivation.A 276-day field trial was set up as a completely randomized design for two types of rice residues, KMD (Bt) and Xiushui 11 (non-Bt parental variety) in triplicate by conventional intensive rice cropping system. The litterbag method was used in the rice residue decomposition and a total of 120 straw and root litterbags were either placed on the soil surface or buried at 10 cm depth in the field on Dec. 24, 2005. The litterbags were sampled periodically and their soil bacterial and fungal communities were determined by terminal restriction fragment length polymorphism (T-RFLP). The additive main effects with multiplicative interaction (AMMI) model were performed for the analysis of T-RFLP on binary variables of peak presence (presence/absence). The analysis of variance and linear regressions were performed for analysis of AMMI data.Total AMMI model analysis revealed that microbial community composition in the litterbags was affected by temporal and spatial factors. Compared with the non-Bt rice residue treatment, Bt rice straw had no significant effects on the soil bacterial and fungal community composition during the study period, regardless of the litterbags being placed on the surface or buried in the soil. There were no significant differences in the bacterial community composition profiles in root decomposition between Bt transgenic and non-Bt varieties. However, significant differences in soil fungal community composition between the buried Bt and non-Bt rice roots were observed in soils sampled on days 31, 68, and 137, indicating that Bt roots incorporated into paddy soil may affect soil fungal community during the initial stage of their decomposition.There were some significant differences in fungal community composition between Bt rice root and non-Bt root treatments at the early stage of root decomposition in the paddy field. It is important that, before Bt rice is released for commercial production, more research should be conducted to evaluate the ecological effects of the Bt rice residues returned to paddy field upon grain harvesting.

Composting is an effective treatment process to realize sludge land application. However, nitrogen loss could result in the reduction of nutrient value of the compost products and the stabilization effect of composting on heavy metal concentration and mobility in sludge has been shown to be very limited.Laboratory-scale experiments were carried out to investigate the effects of bamboo charcoal (BC) on nitrogen conservation and mobility of Cu and Zn during sludge composting.The result indicated that the incorporation of BC into the sludge composting material could significantly reduce nitrogen loss. With 9% BC amendment, total nitrogen loss at the end of composting decreased 64.1% compared with no BC amendment (control treatment). Mobility of Cu and Zn in the sludge may also have been lessened, based on the decline in diethylenetriaminepentaacetic acid-extractable Cu and Zn contents of composted sludge by 44.4% and 19.3%, respectively, compared to metal extractability in the original material.Ammonia adsorption capability of BC might be the main reason for the retention of nitrogen in sludge composting materials. Decrease of extractable Cu2+ and Zn2+ in the composting material mainly resulted from the adsorption of both metals by BC.Incorporation of BC into composting material could significantly lessen the total nitrogen loss during sludge composting. Mobility of heavy metals in the sludge composting material could also be reduced by the addition of BC.Bamboo charcoal could be an effective amendment for nitrogen conservation and heavy metal stabilization in sludge composts. Further research into the effect of BC-amended sludge compost material on soil properties, bioavailability of heavy metals, and nutrient turnover in soil needs to be carried out prior to the application of BC-sludge compost in agriculture.

Genetic modification of commercial crops may affect their decomposition and nutrient cycling processes in agricultural ecosystems. Intensive rice cultivation under partially submerged conditions (paddy rice) is an important and widespread cropping system, particularly in the tropics, yet there is little data on the decomposition of Bt rice residue under field conditions. We investigated straw and root decomposition of rice modified to express the Cry1Ab protein of Bacillus thuringiensis (Bt) to kill lepidopteran pests, compared with a parental non-Bt isoline. The objective of this study was to assess the possible impacts of cry gene transformation of rice on residue decomposition under intensive rice cultivation with long period of submergence.The decomposition experiment was set up as a completely randomized design for two types of rice residues, KMD (Bt) and Xiushui 11 (non-Bt parental variety) in triplicate. All together six plots (4 m × 15 m each) were cultivated in two successive years by conventional intensive rice cropping methods. Litterbags were used to evaluate rice residue decomposition. Two grams of Bt and non-Bt rice roots or 5 g of rice straw were sealed in a 10 × 15-cm nylon mesh litterbag. A total of 192 straw and root litterbags each were prepared. Both kinds of litterbags were then placed either at the surface or buried at 10 cm depth along two parallel transects within each plot in the field on 24 December, 2005. Decomposition dynamics were determined by changes in ash-free mass remaining (AFMR), and nutrient content (C and N) of rice straw and root materials contained in mesh litterbags. Cellulose and lignin contents of the original rice residues were determined according to Van Soest’s methods (1963). The AFMR was recorded by calculating ash weight. Total C (TC) and total N (TN) of the samples were analyzed by combustion in an element autoanalyzer and calculated by multiplying %C and %N by the final weights obtained prior to ashing.AFMR, total carbon, and C:N ratios of the rice residues decreased over time. An increase in total nitrogen was observed at the beginning of straw decomposition, from day 17 to 31. There were no substantial differences in straw decomposition between Bt and conventional rice varieties, but Bt roots in buried litterbags displayed significantly lower AFMR, TN, and TC contents at the initial decomposition stage (day 31, 68, and 137 for AFMR and TC and day 68, 137, and 207 for TN) compared to the conventional rice.The significant differences which were detected at the initial decomposition may not result from the expression of the cry1Ab gene. It is more likely that the genetic transformation or the effect of inserting foreign genes may result in differences between Bt and non-Bt rice with respect to chemical composition of rice plant residues. Although there were no statistically significant differences in total lignin or total cellulose content between Bt and non-Bt rice roots, we speculate that significant differences in the decay rate between buried Bt and non-Bt rice roots observed at the early stage of the experiment could result from a variation in the availability of readily metabolizable root components of the transgenic rice roots due to transformation or site effects of the insertion of foreign genes.This is the first report regarding decomposition of Bt rice residue (straw and root) under field conditions. In the traditional rice–rice cropping system, we found no substantial differences of rice straw decomposition between transgenic Bt and conventional near-isogenic variety. However, some statistically significant differences in decompositional properties, such as AFMR, TN, and TC contents between Bt transgenic and non-Bt parental rice roots, were found under buried condition before the end of first rice season. Our results obtained in two consecutive years in the field indicated that Bt transgenic rice root decomposed relatively faster than that of the non-Bt parental rice root under buried condition in the first 200 days.Although genetic modification of plants can offer many benefits, the planting of transgenic crops has raised a number of concerns, including the ecological impact of these plants on decomposition and nutrient cycling processes in agriculture ecosystems. Our results obtained over two consecutive years suggested that the insertion of the cry1Ab gene into the rice genome might result in increasing the rate of rice root decomposition in paddy fields. Attentions need to be paid to the ecological impacts of this phenomenon, especially on nutrient cycling and methane production and flux after its successive incorporated into soil upon harvest. Further studies in the dynamics of the biota associated with root residues is of great significance in assessing its potential effects on microbe-mediated processes and functions in soil.

Two kinds of common turfgrass, fescue and ryegrass, were grown in soils amended with 20 × 80% sludge compost (SC) in this research. The effects of SC on two kinds of soil and response of fescue and ryegrass to the SC amendment were studied. The results showed that urease activity, extractable content of Cu and Zn and Electrical conductivity of both soils increased while pH decreased with the increase of SC amendment. However, the change of these parameters also depended strongly on soil characteristics. Sludge compost at the ≤40 and ≤60% levels can improve growth of fescue and ryegrass, respectively. The biomass of fescue grown in substrate with 40% SC increased 27% in a red soil and 44% in a yellow loamy soil compared to the control. The biomass of ryegrass grown in substrate with 60% SC increased 120% in the red soil and 86% in the yellow loamy soil. Sludge compost amendment at these levels did not significantly affect soluble salt contents of soil or Cu and Zn in plant tissue. Therefore, rational use of sludge compost can take advantage of its beneficial effect as a nutrient source for plant production while avoiding the potential deleterious effects on soil and plant.

Municipal solid waste (MSW) landfills are one of the major sources of offensive odors potentially creating annoyance in adjacent communities. At the end of May 2007, an odor pollution incident occurred at the Tianziling landfill site, Hangzhou, China, where the residents lodged complaints about the intense odor from the landfill, which drew a significant attention from the government. In this study, ambient air monitoring was conducted at the Tianziling landfill site. The main odor composition of the gas samples collected on June 1st 2007 and the reduction of various odorous gases from the samples collected on June 1st 2009 due to the applied odor control techniques were determined using gas chromatography-mass spectrometry (GC-MS). In addition, variations of primary odorous gaseous (NH3 and H2S) concentrations at different locations in the landfill site from July 2007 to June 2009 were also investigated by using classical spectrophotometric methods. Results showed that a total of 68 volatile compounds were identified among which H2S (56.58–579.84 μg/m3) and NH3 (520–4460 μg/m3) were the notable odor components contributing to 4.47–10.92% and 83.91–93.94% of total concentrations, respectively. Similar spatial and temporal shifts of H2S and NH3 concentrations were observed and were significantly affected by environmental factors including temperature, air pressure and wind direction. Odor pollution was worse when high temperature, high humidity, low air pressure, and southeast, northeast or east wind appeared. Moreover, the environmental sampling points of the dumping area and the leachate treatment plant were found to be the main odor sources at the Tianziling landfill site. The odor control technologies used in this project had a good mitigating effect on the primary odorous compounds. This study provides long-term valuable information concerning the characteristics and control of odors at landfill sites in a long run.Highlights► Characterization and control effect of odor at Tianziling landfill were investigated. ► 68 odors in 10 classes were identified. ► Dumping area and leachate treatment plant were the main odor sources. ► Spatial and temporal shifts of odors were affected by environmental factors. ► Odor control engineering had a good effect on removal of primary odor concentrations.

•A pilot-scale A2O-MBR system treating textile auxiliaries wastewater was assessed.•Organic matter and recycle ratio strongly affected the performance of the system.•GC/MS analysis found some refractory organics in the MBR permeate.•Combination of organic foulants and inorganic compounds caused membrane fouling.The removal of organic compounds and nitrogen in an anaerobic–anoxic–aerobic membrane bioreactor process (A2O-MBR) for treatment of textile auxiliaries (TA) wastewater was investigated. The results show that the average effluent concentrations of chemical oxygen demand (COD), ammonium nitrogen (NH4+–N) and total nitrogen (TN) were about 119, 3 and 48 mg/L under an internal recycle ratio of 1.5. The average removal efficiency of COD, NH4+–N and TN were 87%, 96% and 55%, respectively. Gas chromatograph–mass spectrometer analysis indicated that, although as much as 121 different types of organic compounds were present in the TA wastewater, only 20 kinds of refractory organic compounds were found in the MBR effluent, which could be used as indicators of effluents from this kind of industrial wastewater. Scanning electron microscopy analysis revealed that bacterial foulants were significant contributors to membrane fouling. An examination of foulants components by wavelength dispersive X-ray fluorescence showed that the combination of organic foulants and inorganic compounds enhanced the formation of gel layer and thus caused membrane fouling. The results will provide valuable information for optimizing the design and operation of wastewater treatment system in the textile industry.