Environmental impacts of cement kiln co-incineration sewage sludge biodried products in a scale-up trial

The biodrying technology as a pretreatment technology can overcome the limitations of cement kilns co-incineration sewage sludge (SS) on energy consumption. But the impact of SS biodried products on cement kilns and the route carbon reduction potential of biodrying + cement kilns have not been studied. In this study, SS biodrying and cement kiln co-incineration biodried product trials were conducted to highlight the matrix combustion characteristics, and the impact of biodried products on cement kilns (clinker capacity, coal consumption, and pollutant discharge). The carbon emissions of the four scenarios were assessed based on these results. The results showed that water removal rate reached 65.5 % after 11-day biodrying, and the wet-based lower heating value of the biodried product increased by 76.0 % compared with the initial matrix. Comprehensive combustibility index of the biodried product (0.745 × 10-7 %2℃-3min-2) was better than that of SS (0.433 × 10-7 %2℃-3min-2) although a portion of the organic matter was degraded. Cement kiln co-incineration of biodried products (150 t/d) resulted in per tonne of clinker saved 5.61 kg of coal due to the heat utilization efficiency of biodried products reached to 93.7 %. However, it led to an increase in the emission concentrations of NOX and SO2. Assessment results indicated that the biodrying + cement kiln pathway reduced CO2 emissions by 385.7 kg/t SS. Biodried products have greater potential to reduce emissions as alternative fuels than as fertilizers. This study indicated the advantages of SS biodrying + cement kiln co-incineration route.

Comprehensively assessing priority odorants emitted from swine slurry combining nontarget screening with olfactory threshold prediction

The lack of one-to-one olfactory thresholds (OTs) poses an obstacle to the comprehensive assessment of priority odorants emitted from swine slurry using mass spectrometric nontarget screening. This study screened out highly performing quantitative structure-activity relationship (QSAR) models of OT prediction to complement nontarget screening in olfactory perception evaluation. A total of 27 compounds emitted at different slurry removal frequencies were identified and quantified using gas chromatography-mass spectrometry (GC-MS), including thiirane, dimethyl trisulfide (DMTS), and dimethyl tetrasulfide (DMQS) without OT records. Ridge regression (RR, R2 = 0.77, RMSE = 0.93, MAE = 0.73) and random forest regression (RFR, R2 = 0.76, RMSE = 0.97, MAE = 0.69) rather than the commonly used principal component regression (PCR) and partial least squares regression (PLSR) were used to assign OTs and assess the contributions of emerging volatile sulfur compounds (VSCs) to the sum of odor activity value (SOAV). Priority odorants were p-cresol (25.0-58.9 %) > valeric acid (8.3-31.7 %) > isovaleric acid (6.7-19.0 %) > dimethyl disulfide (4.7-15.7 %) > methanethiol (0-13.6 %) > isobutyric acid (0-8.6 %), whereas the contributions of three emerging VSCs were below 10 %. Vital olfactory active structures were identified by QSAR models as having high molecular polarity, high hydrophilicity, high charge quantity, flexible structure, high reactivity, and a high number of sulfur atoms. This protocol can be further extended to evaluate odor pollution levels for distinct odor sources and guide the development of pertinent deodorization technologies.

Intercropped Amygdalus persica and Pteris vittata applied with additives presents a safe utilization and remediation mode for arsenic-contaminated orchard soil

Intercropping the arsenic (As) hyperaccumulator Pteris vittata with fruit trees can safely yield peaches in As-polluted orchards in South China. However, the soil As remediation effects and the related mechanisms of P. vittata intercropped with peach trees with additives in the north temperate zone have rarely been reported. A field experiment was conducted to systematically study the intercropping of peach (Amygdalus persica) with P. vittata with three additives [calcium magnesium phosphate (CMP), ammonium dihydrogen phosphate (ADP), and Stevia rebaudiana Bertoni residue (SR)] in a typical As-contaminated peach orchard surrounding a historical gold mine in Pinggu County, Beijing City. The results showed that compared with monoculture (PM) and intercropping without addition (LP), the remediation efficiency of P. vittata intercropping was significantly increased by 100.9 % (CMP) to 293.5 % (ADP). CMP and ADP mainly compete with available As (A-As) adsorbed to the surface of Fe-Al oxide through PO₄^3-, while SR might activate A-As by enhancing dissolved organic carbon (DOC) in P. vittata rhizospheres. The photosynthetic rates (G_s) of intercropped P. vittata were significantly positively correlated with pinna As. The intercropping mode applied with the three additives did not obviously affect fruit quality, and the net profit of the intercropping mode (ADP) reached 415,800 yuan·ha^-1·a^-1. The As content in peaches was lower than the national standard in the intercropping systems. Comprehensive analysis showed that A. persica intercropped with P. vittata applied with ADP is better than other treatments in improving risk reduction and agricultural sustainability. In this study, a theoretical and practical basis is provided for the safe utilization and remediation of As-contaminated orchard soil in the north temperate zone.

Cadmium accumulation responses in Hylotelephium spectabile: The role of photosynthetic characteristics under different nitrogen, moisture, and light conditions

The influence of environmental factors on Cd accumulation by Hylotelephium spectabile and its physiological mechanisms are unclear. A field trial was conducted to investigate the effects of nitrogen, soil moisture, and light regulation on plant growth, Cd absorption and translocation, and the photosynthetic characteristics of two H. spectabile populations (LN with high Cd accumulation capacity and HB1 with relatively low Cd accumulation capacity). The results showed that Cd accumulation in LN was 59.6% higher than that in HB1 which may partly be explained by the inherent high transpiration rate of LN, especially at the terminal stage. In addition, the photosynthetic rate of LN responded more positively to nitrogen than HB1, which further amplified its advantages on plant growth and Cd accumulation. Moderate drought significantly stimulated root growth of LN, indicating that LN possesses stronger resistance to drought. Shade inhibited Cd distribution, rather than directly affecting Cd concentrations in H. spectabile. The combined stress of shade and drought had a synergistic effect on Cd translocation in H. spectabile. Moreover, LN achieved 17.3%∼444.5% higher transpiration levels than HB1 under environmental stress, which ensured a more efficient Cd transport capacity of LN. Therefore, the investigation of photosynthetic characteristics further revealed the physiological mechanism by which LN accumulated Cd superior to HB1 under environmental stress and responded more positively to nitrogen nutrition.

Insights into the effect mechanism of back-mixing inoculation on sewage sludge biodrying process: Biodrying characteristics and microbial community succession

Back mixing was frequently used to replace conventional bulking agenting, however, however, the internal effect mechanism was unclear. This study compared four bulking agents: mushroom residue (MR), MR + primary BM (BM-P), BM-P, and secondary BM (BM-S). The effect mechanism of back mixing (BM) inoculation was assessed based on biodrying performance and microbial community succession. Four trials (Trial A, Trial B, Trial C, and Trial D) reached maximum temperatures of 61.9, 68.8, 73.7, and 69.9 °C on days 6, 3, 2, and 2, respectively. Application of BM increased pile warming rate and resulted in higher temperatures. Temperature changes and microbial competition lead to decline in microbial diversity and richness during the biodrying process. Microbial diversity increased of four biodried products. The number of microorganisms shared by Trial A, Trial B, Trial C, and Trial D were 90, 119, 224, and 300, respectively. The addition of BM improved microbial community stability, and facilitating the initiation of biodrying process. Microbial genera that played an important role in the biodrying process included Ureibacillus, Bacillus, Sphaerobacter, and Tepidimicrobium. Based on these results, it was concluded that BM was efficient method to enhanced the microbial activity and reduced the usage of bulking agent.

The impact of land use and land cover changes on the landscape pattern and ecosystem service value in Sanjiangyuan region of the Qinghai-Tibet Plateau

Decades of intensifying human activities have caused dramatic changes in land use and land cover (LULC) in the ecologically fragile areas of the Qinghai-Tibet Plateau, which have led to significant changes in ecosystem service value (ESV). Taking the ecologically fragile Sanjiangyuan region of the Qinghai-Tibet Plateau as the research object, we focused on understanding the impact of LULC changes on the Sanjiangyuan's landscape pattern and its corresponding ESV, which was combined with a Markov-Plus model to predict LULC changes in 2030. The results showed: (1) from 2000 to 2020, the LULC of Sanjiangyuan has changed to varying degrees, respectively. In the central and southern regions where animal husbandry is the mainstay activity, the area of grass land converted to bareland had expanded; (2) from 2000 to 2010, the total regional ESV increased sharply. However, the total amount of ESV decreased from 2010 to 2020; (3) the overall ESV in the study area was observed to be trending down and is expected to decrease by approximately 4.25 billion CNY by 2030; (4) the fragmentation and complexity of regional landscape patterns will negatively affect local ecosystem stability and biodiversity. Overall, there is a strong temporal and spatial correlation between LULC and ESV. This study will provide a reference for the local government to provide targeted and sustainable land management policies, thereby promoting the improvement of the Qinghai-Tibet Plateau regional ecology value.

Exploring the influence mechanisms of polystyrene-microplastics on sewage sludge composting

To explore the influence mechanisms of polystyrene-microplastics (PS-MPs) on sewage sludge composting and put forward relevant composting adjustment strategies, a 30-day sewage sludge (SS) composting experiment was conducted by adding 0%, 0.5%, and 1% (w/w) PS-MPs. The addition of PS-MPs reduced compost temperature, microbial biomass carbon (MBC), and the degradation of volatile solids (2.6%-4.8%), and inhibited the activities of key enzymes (β-glucosidase and alkaline phosphatase) but increased urease activity in the thermophilic phase. Moreover, PS-MPs altered the relative abundance of dominant bacteria and changed the relevance of main enzymes and bacterial communities. Moreover, high levels of PS-MPs inhibited the contribution of dominant bacterial to alkaline phosphatase and β-glucosidase. Redundancy analysis revealed that PS-MPs affected the composting process mainly through reduced MBC at the mesophilic phase and temperature at the thermophilic phase. Thus, regulating MBC and temperature in specific phases could help overcome the adverse effects of PS-MPs on composting.

[Distribution Characteristics and Risk Assessment of Heavy Metal Pollution in Farmland Soils and Crops in Luancheng, Shijiazhuang City]

In order to explore the distribution characteristics of heavy metal contamination of farmland soil surrounding Luancheng town, Shijiazhuang City, Henan province, the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the surface soil and crops were determined and assessed. The principal components were also analyzed for source apportionment. The heavy metal concentrations in crops were further detected, and the non-carcinogenic health risks in the study area were evaluated using the probabilistic risk assessment method, as to provide a theoretical basis for the treatment, prevention, and control of heavy metal pollution in farmland soil in Luancheng. According to the results, ω(Cd), ω(Cr), ω(Cu), ω(Pb), and ω(Zn) in the soils were 0.06-1.08, 22.14-473.47, 12.83-150.74, 10.75-577.72, and 62.23-652.78 mg·kg^-1, which exceeded the standard with over-standard rates reaching 1.83%, 1.22%, 0.61%, 0.61%, and 1.22%, respectively. Further, Cd and Pb were transported into crops, in which Cd concentrations exceeded the standard in some corn samples, and Cd and Pb concentrations exceeded the standard in some wheat samples. The total non-carcinogenic health risks (TTHQ) to the human body caused by the consumption of heavy metals in corn grown in the study area were all less than 1, with no obvious negative effects, and TTHQ was higher than 1 in wheat, increasing the likelihood of negative impacts on the human body. With the influence of the distribution of pollution-related enterprises in the industrial zone, heavy metal concentrations were higher in the south, west, and middle directions of the study area. Among them, the study area soil was slightly contaminated by Cd (Level 1). Cd and Hg had a slight potential ecological risk (Level 2), whereas other heavy metals had low potential ecological risk (Level 1). In general, most of the surface cultivated soil was not obviously polluted by heavy metals in the study area. According to the PMF results and survey, we speculated that soil heavy metals mainly came from soil parent material (52.05%), artificial pollution sources (historical sewage irrigation and industrial manufacture) (32.98%), and atmospheric deposition (14.97%). To summarize, the study area should be divided into a priority protection category and safe utilization category. The input of pollution sources should be strictly controlled for the priority protection category, and alternative planting, rotating, and fallow should be implemented for the safe utilization category to reduce the risk of standard-exceeding agricultural products.

Correlation of microbial dynamics to odor production and emission in full-scale sewage sludge composting

Odor is inevitably produced during sewage sludge composting, and the subsequent pollution hinders the further development of composting technologies. Third-generation high-throughput sequencing was used to analyze microbial community succession, and the correlations between odor and microbial communities were evaluated. Hydrogen sulfide (47.5-87.9 %) and ammonia (9.4-49.9 %) contributed majorly to odor emissions, accounting for 93.7-98.5 % of the emissions. Volatile sulfur compounds were mainly produced in the mesophilic and pre-thermophilic phases (43.0-83.4 %), whereas ammonia was mainly produced in the thermophilic phase (52.1-59.4 %). Microorganisms dominant in the mesophilic and thermophilic phases correlated positively with odor production in the following order: Rhodocyclaceae > Clostridiaceae_1 > Hyphomicrobiaceae > Acidimicrobiales > Family_XI, whereas those dominant in the cooling phase showed negative correlations with odor production in the following order: Bacillus > Sphingobacteriaceae > Pseudomonadaceae > DSSF69 > Chitinophagaceae. The back mixing of mature compost is expected to serve as an economical measure for controlling odor during sewage sludge composting.

Assessing the quality of the soil around a shale gas development site in a subtropical karst region in southwest China

The construction of shale gas facilities disturbs large areas of land and affects soil quality and function. In this study, we investigated the properties (including physical, chemical, and microbiological indicators) of soil at three different distances from a shale gas development site (<30 m, 30-50 m, and 50-100 m) in a karst area in 2017 and 2020. Our results showed that the soil water content; available carbon, nitrogen, and phosphorus concentrations; total nitrogen and total phosphorus concentrations; microbial biomass, and enzyme activities increased (P < 0.05) as the distance from the well pad increased, and the total carbon content, pH, electrical conductivity, and some ions (magnesium, sodium, and potassium) decreased with distance from the well pad (P < 0.05). The differences in the soil properties were most noticeable in 2017. The increases in the available nutrients were greater than in the total nutrients. The overall soil quality after the shale gas well pad construction was limited by the microbial biomass and sodium contents. The soil properties recovered most quickly at 30-50 m from the well pad, because of local farmland management practices that improved the soil properties and microbial biomass, and reduced the microbial stress. Therefore, we recommend planting sodium-tolerant crops on the land closest to the well pads, to facilitate restoration of the soil that was disturbed during the construction period.

How newly developed shale gas facilities influence soil erosion in a karst region in SW China

We already know that the construction of shale gas extraction infrastructure exacerbates soil erosion in vulnerable areas. We are not clear however, about whether the completed well pads and pipelines continue to influence soil erosion after the construction is completed. We applied high-resolution remote sensing images and DEM data from 2014 and 2017 and the Revised Universal Soil Loss Equation (RUSLE) model to calculate how the layout of the well pads and pipelines in a shale gas development area affected soil erosion. We used Geodetector to analyze the factors that affected the soil erosion intensity around the well pads. The results showed that about 0.02% and 0.12% of the total erosion in the shale gas development zone was directly caused by the completed well pads and pipelines in 2014 and 2017, respectively. Most of the erosion was related to the completed pipelines. The completed shale gas well pads affected the soil erosion intensity up to 90 and 60 m from the pads in 2014 and 2017, respectively. The soil erosion around the completed pipelines was mainly from the soil surface over the pipeline and had little effect on the surroundings. The main influences on the soil erosion intensity at different distances from the well pads were land use and slope, and the interactions between them. We suggest that, when developing new shale gas extraction facilities, gas pipelines should be arranged in gently sloping areas, and vegetation should be planted on the bare soil over the pipelines to reduce soil erosion.

Water-heat balance characteristics of the sewage sludge bio-drying process in a full-scale bio-drying plant with circulated air

Sewage sludge bio-drying technology has attracted considerable attention in recent years. In this study, we explored the water-heat balance under two ventilation strategies for the first time in bio-drying plants with circulated air, and examined the influence of air circulation on water removal and heat recovery. We want to obtain the relationships of pile temperature, ventilation, and water removal. Then, it provides support for optimizing the bio-drying process conditions and improving the efficiency through analysis of the water-heat relationship. In the low-ventilation and high-ventilation trials, water removed was mainly on Days 9-12 and 1-4, respectively. Ventilation and pile temperature jointly determine the water removed during the bio-drying process. Water balance indicated that more than 30% of the water was removed under the nonventilated process. More organic matter was degraded to maintain a higher pile temperature under low-ventilation than under high-ventilation, which also led to more radiation heat being lost. High-ventilation trial input less energy (3.36 MJ/kg water removed) but obtained a higher bio-drying index I (7.04) and heat utilization efficiency Qeffic (94.1%). Heat balance showed that lower energy consumption by dry air (Qdryair) was obtained due to circulation air with high temperature. Circulation air also has a higher carried capacity of water vapor but carries more water into the pile due to higher humidity.

Safe utilization of cadmium- and lead-contaminated farmland by cultivating a winter rapeseed/maize rotation compared with two phytoextraction approaches

Compared with phytoextraction, growing suitable crops may be a more profitable and practical approach for managing contaminated farmland, especially when there are multiple pollutants. In this 5-year field study, the phytoaccumulator Hylotelephium spectabile, the high-biomass species amaranth (Amaranthus hypochondriacus), and a winter rapeseed/maize rotation crop were cultivated on farmland contaminated with cadmium (Cd) and lead (Pb). Over 4 consecutive years, the annual Cd uptake and extraction efficiency of H. spectabile was 117.6 g hm^-2 and 2.36%, respectively. The Cd extraction efficiency of amaranth was equivalent to that of H. spectabile because of its high biomass, and it extracted more Pb (660-2210 g hm^-2) from the soil than did H. spectabile. However, neither of these species was able to remediate contaminated farmland rapidly and inexpensively, even with enhancing strategies such as variety screening and the addition of fertilizers and a chelating agent. A safe utilization approach to cultivate rapeseed instead of wheat significantly reduced the carcinogenic and noncarcinogenic risks. The concentrations of heavy metals in rapeseed oil were below the limits specified in the Chinese national food standard, and the heavy metal concentrations in the byproducts (rapeseed meal and straw) were below the limits specified in Chinese national standards for organic fertilizer and feed. The cost of safe utilization was one-quarter that of phytoextraction, and the net economic benefit was 33.5%-123.5% higher than that of wheat crops. Therefore, the rapeseed/maize rotation is a profitable and feasible approach for the safe utilization of Cd- and Pb-contaminated farmland on the northern plains of China.

Life cycle and economic assessment of enhanced ecological floating beds applied water purification

The ecological floating beds (EFB) are widely used in water quality restoration because of its low cost, high efficiency, and green characteristics. However, there is a potential impact of the EFB on the environment while water purification is not in progress. In this study, the life cycle assessment (LCA) and life cycle cost (LCC) methods were used to evaluate the overall environment of mixed-fill and biofilm enhanced EFB. The results show that the total environmental impact of the mixed-fill ecological floating beds (MEFB) is greater than that of the biofilm ecological floating beds (BEFB). In the raw material acquisition and operational stages, the environmental impact of the MEFB is smaller than that of the BEFB, while the environmental impact of the MEFB during the construction phase is much greater than that of the BEFB. The environmental impact of the construction stage of the MEFB accounts for 98.3% of the environmental impact of the entire life cycle. The operational stage of the MEFB was eco-friendly with regard to eutrophication potential, photochemical oxidation potential, ozone layer depletion potential, human toxicity potential, freshwater aquatic eco-toxicity potential, and terrestrial eco-toxicity potential environmental impact, and these effects of the operational stage of the MEFB account for 45.5% of the total environmental impact. The impact of the BEFB on the environment during raw material acquisition, construction, and operation accounts for 46.7%, 37.7%, and 15.6%, respectively, of the entire life cycle impact. Both two EFB technologies, the capital cost was the main expenditure with LCC, accounting for 60.4% and 52.9% of the MEFB and BEFB, respectively.

Fate and biodegradation characteristics of triclocarban in wastewater treatment plants and sewage sludge composting processes and risk assessment after entering the ecological environment

Triclocarban (TCC) has a high detection frequency in soil, rivers, sediments, and organisms, and its ecological risks have attracted substantial attention. In this study, we analyzed the fate of TCC in four wastewater treatment plants (WWTPs) in Zhengzhou, China, the biodegradation characteristics during the composting process, and the ecological risks of TCC when entering different environmental compartments. The concentration of TCC in the influent was 731.1-812.4 ng/L. More than 53.4% of TCC was biodegraded during the wastewater treatment process, and less than 2.5% was retained in the effluent. TCC was effectively removed through microbial degradation and sewage sludge absorption, and there were only minor differences in the different wastewater treatment processes. It is worth noting that more than 38% of TCC was enriched in sewage sludge (1430.1-1663.8 ng/g). The corresponding biodegradation rates of TCC were 65.7% and 82.8% in sewage sludge after 17 days of composting treatment with sawdust and straw as bulking agents, respectively. The estimated results showed that effluent discharge into the city rivers was safe. Composting could effectively degrade TCC and decrease the ecological risk of TCC when applied to sewage sludge.

Influence of shale gas development on core forests in the subtropical karst region in southwestern China

Core forests are an important component of forest landscapes and wildlife habitat. Although the core forests were damaged during the development of shale gas sites, it remain unclear how much damage the shale gas development has caused to this ecologically vulnerable region. We analyzed high-resolution remote sensing images of a shale gas development area in 2012, 2014, and 2017 in the karst region in southwestern China. The results showed that the core forest area decreased by approximately 4.0% from 2012 to 2017. Of this decrease, approximately 32.3% was related to the shale gas development activities, while 67.7% was related to other human activities, i.e., agricultural lands and residential developments. Approximately 5.6% of the decrease in the core forest was for new pipelines, with 0.5 ha occurred in 2012-2014 and 248.6 ha occurred in 2014-2017. Of the shale gas development activities, the pipeline constructions were most detrimental to the core forest. The patchiness of the core forest increased by 8.2% from 2012 to 2017 by the expansions of dry fields, towns, and settlements. The core forest Effective Mesh Size (MESH) decreased by 86.3%, primarily caused by the shale gas development pipelines. In conclusion, human activities that were not directly related to shale gas development were the main driver of the core forest decreases. The pipelines caused most losses of the core forest among the shale gas activities and the impacts deteriorated as the shale gas development proceeds. Therefore, we propose that new shale gas pads should be placed adjacent to existing shale gas pipelines and new shale gas pipelines should be constructed in parallel with existing roads to reduce the damages on core forest.

Use of life cycle assessment and water quality analysis to evaluate the environmental impacts of the bioremediation of polluted water

The lakes along the Yangtze River are important source of pollutants that ultimately flow from the river into the East China Sea. Bioremediation is a green technology used to treat polluted water in lakes along the Yangtze River. Life cycle assessment and a comprehensive water quality index are used to evaluate the potential environmental impacts of constructed wetlands (CWs), ecological floating beds (EFBs), and combined ecological floating beds (CEFBs). The results showed that the raw material acquisition, construction, and operation of the CWs, EFBs, and CEFBs accounted for 24.1%, 35.3%, and 40.6%, respectively, of the total environmental impact. The acquisition of raw materials to construct the bioremediation system accounted for 51.6% of the total environmental impact. Among the nine impact categories considered, the system's global warming potential was the largest. Among the three stages of the project (raw material acquisition, construction, and operation), construction had the largest impact on eutrophication (the eutrophic potential of the construction stage was the largest). Furthermore, the operation of the project reduced the human eco-toxicity potential. The evaluation of the water quality before and after implementing the project revealed that CEFBs purified the water more effectively than CWs and EFBs did, particularly with respect to the removal of the total phosphorus.

Ecological adaptability and population growth tolerance characteristics of Carex cinerascens in response to water level changes in Poyang Lake, China

Water level conditions are the key factors that affect the growth and distribution of wetland plants. Using Carex cinerascens (C. cinerascens) as the study species, we employ indoor simulations and field surveys. Our results show that C. cinerascens can adapt to rhythmic changes in the water level through different adaptation strategies. Compared to that of the control group, plant growth was better with a 0-0.4 cm/d water level rate, and plant growth was in the 42-56 cm range to that a 1.0-1.4 cm/d water level rate. Furthermore, it was observed that 0-0.4 cm/d was the most suitable growth rate, with 0.6-1.0 cm/d and 0-32 cm being the ideal plant tolerance ranges, and increasing to 1.0-1.4 cm/d and 32-56 cm exceeds the plant tolerance threshold. In the middle and late period of the experiment (25-45 d), the ecological characteristics of the plants changed significantly. For example, the root-to-shoot ratio of the plant in the stable water level reached 26.1. In our field observations, plant biomass can be influenced by a variety of environmental factors. The frequency of the species was the largest at an elevation of 15 m, and the growth status of the dominant and companion species of C. cinerascens was weakened with an increase in soil moisture content. The suitable water content for C. cinerascens growth was 27.6-57.3%, the distribution elevation was 12.54-16.59 m, and the optimum elevation was 13.56-15.54 m. The study is expected to provide a reference for wetland ecology research and wetland protection and restoration, a theoretical reference for the coordination of water resource development and utilization of Poyang Lake and ecological protection of important lakes and wetlands, and an important scientific basis for wetland hydrologic regulation, ecological restoration and biodiversity conservation.

[Spatial Distribution and Risk Assessment of Heavy Metal Pollution in Farmland Soils Surrounding a Typical Industrial Area of Henan Province]

In order to fully explore the spatial distribution of soil heavy metal contaminants in farmland soil surrounding a typical industrial area in Dakuai town, Xinxiang city, Henan Province, the concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn in the surface soil and within the soil profile were determined and assessed. The principal components were also analyzed for source apportionment to provide a theoretical basis for the control and prevention of heavy metal pollution. According to the results, the soils in the study area are severely contaminated by Cd and Cu and moderated contaminated by As due to the battery manufacture and Cu (e.g., pipe and wire) processing. The concentrations of Cd, Cu, and As in soils were (2.56±1.23) mg·kg^-1, (205.58±157.49) mg·kg^-1, and (15.27±4.14) mg·kg^-1, respectively, which exceeds standards by 100%, 89.44%, and 3.40%, respectively. Accounting for the influence of pollution sources, terrain, runoff erosion, and prevailing wind direction, all heavy metal concentrations were higher in the south direction, lower in the north direction. The concentrations of Cd and Cu in soil profile samples decreased with depth, with highest concentrations at the surface, indicating the strong effect of industrial activities. Arsenic concentrations varied little with soil depth due to its strong migration ability in alkaline soil, again suggesting an industrial source. Among them, the soil of study area was severely contaminated by Cd and Cu (Level 5). Cd poses a severe potential ecological risk (Level 5) and Cu poses a medium risk (Level 2) in the study soils, while other heavy metals show low potential ecological risk (Level 1). The order of the risk identified was Cd > Cu > Ni > As > Pb > Cr > Zn. In addition, the combined potential ecological risk of heavy metals in the target area is severe. The principal component analysis showed that the high As, Cd, and Cu contents are mainly derived from industrial areas. Therefore, it is urgent to remediate Cd and Cu soil contamination in this area and implement precautions to limit As contamination.

Effects of lactic acid on modulating the ammonia emissions in co-composts of poultry litter with slaughter sludge

The aim of this work was to study the feasibility of lactic acid addition during poultry litter and slaughter sludge composting for controlling NH₃ emissions. The results indicated that lactic acid addition reduced NH₃ emissions and promoted the maturity of the composting product. Compared to the blank, nitrogen loss in the form of NH₃ emissions in the 0.4%, 0.7%, and 1.0% lactic acid treatments decreased by 3.36%, 8.29%, and 14.65%, respectively. Moreover, lactic acid addition promoted the relative abundance of Lactobacillales, while the microbial community of the blank was dominated by Bacillales. The mechanism behind the control of NH₃ emissions via the addition of lactic acid involved the secretion of large amounts of lactic acid by Lactobacillales, which lowers the pH of the initial compost pile. This study suggests that lactic acid is a suitable additive for composting.

[Effect of Nutrient Regulation and Control on Cd Accumulation Efficiency of Hylotelephium spectabile Under Field Conditions]

A field experiment with an orthogonally designed experiment L9(3⁴) was designed to investigate the effect of different N, P, and K levels on plant growth and Cd uptake by Hylotelephium spectabile. The results showed that the biomass of H. spectabile significantly increased with the N application rate. The highest dry weight in the shoot occurred in the treatments with a high level of N (337.5 kg ·hm^-2), which was 0.86-2.00 times higher than the value with no fertilizer treatment. The addition of K contributed to promoting the Cd absorption of H. spectabile, while no effect was observed when N and P were added. Consequently, NPK fertilizers contribute to increasing the Cd uptake of H. spectabile, and the N and K fertilizer play important role in plant growth and Cd absorption respectively. Moreover, the effect of fertilizers on Cd uptake of H. spectabile was in the order of N > K > P, which indicated that N fertilizer was the main factor for promoting the Cd phytoextraction efficiency of H. spectabile by increasing the biomass. Therefore, the application of high levels of N combined with moderate levels of P and K will be an effective approach to improve the Cd phytoremediation efficiency of H. spectabile by promoting its growth, and the Cd uptake can be increased by a factor of 0.9-2.2 compared to no fertilizer treatment condition.

Effects and interactions of cadmium and zinc on root morphology and metal translocation in two populations of Hylotelephium spectabile (Boreau) H. Ohba, a potential Cd-accumulating species

The interactions between Cd and Zn in their effects on plants are inconsistent and difficult to predict. A hydroponic experiment was conducted to investigate the effects of Cd and Zn and their interactions on root morphology and metal translocation in two populations of Hylotelephium spectabile (Boreau) H. Ohba (Crassulaceae, HB1 and HB2). Both populations showed relative tolerance to high levels of Cd and Zn, except that the leaf biomass of HB1 significantly decreased by 44.6% with 5-mg/L Cd plus 10-mg/L Zn. Root growth was inhibited in both populations by addition of 20-mg/L Zn under Cd stress, while 10-mg/L Zn showed little impact on the root growth inhibition of HB2. Roots with diameter 0.1-0.4 mm contributed most of the total root length (RL) and root surface area (RSA) of H. spectabile. In both populations, these root parameters showed greater suppression with the combined stress of Cd plus Zn than under Cd or Zn single stress, except by adding 10-mg/L Zn under Cd stress. Moreover, HB2 maintained relatively higher RL and RSA than HB1 under the different treatments, which implied that HB2 might possess a more effective mechanism than HB1 for coping in response to Cd and Zn stress. The addition of Zn not only affected the absorption of Cd but also significantly affected the distribution of Cd in different tissues of H. spectabile. A low level of Zn led to increased Cd in the stem of HB2, but an increase in Cd in the leaf and root of HB1. Addition of 10-mg/L Zn led to a significant increase by 188% and 170% in Cd accumulation in aboveground part of HB2 under 2- and 5-mg/L Cd stress, whereas the addition of Zn had little effect on Cd accumulation in HB1. Thus, strong positive interactions of Cd and Zn occurred in HB2, which showed great potential for application in phytoremediation of soil contaminated with both Cd and Zn, warranting further investigation under field condition.

Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments

As an efficient and cost-effective biological treatment method for sewage sludge, composting has been widely used worldwide. To passivate heavy metals and enhance the nutrient content in compost, in the present study, phosphate rock, calcium magnesium phosphate, and monopotassium phosphate were added to the composting substrate. According to the Community Bureau of Reference sequential extraction procedure, phosphate rock and monopotassium phosphate amendments exhibit a good passivation effect on Cd and Pb. The X-ray diffraction patterns proved the formation of Pb₃(PO₄)₂ and Cd₅(PO₄)₂SiO₄ crystals, and X-ray absorption near-edge structure spectroscopy illustrated the change in P speciation after phosphate amendment. Furthermore, phosphate amendment increased the contents of total P and available P, and it reduced the loss of N during sewage sludge composting. The germination index showed that the target phosphate amendments in sewage sludge compost had no negative effects on seed germination, and this method has great potential to be used as a soil amendment.

Perlite as the partial substitute for organic bulking agent during sewage sludge composting

Composting is an efficient and cost-effective technology for sewage sludge treatment, and bulking agents are essential in sewage sludge composting. In this study, perlite was chosen as inorganic bulking agent to partially substitute for the organic bulking agent. Variations in the temperature, bulk density, moisture content, pH, electrical conductivity, organic carbon, nitrogen, phosphorus and potassium were detected during sewage sludge composting. The treatment with a mass ratio of spent mushroom substrate to perlite at 3:1 exhibited the highest pile temperature and the best effect on reducing bulk density and moisture content. In addition, Fourier transform infrared spectra showed that perlite promotes the degradation of organic matter during the composting process, and the germination index showed that the compost from all treatments was safe for agricultural application. When the mass ratios of spent mushroom substrate and perlite at 3:1 and 2:2 were chosen as bulking agents, the sewage sludge compost product could be used to produce plant cultivation substrate, and economic benefits could be obtained from sewage sludge composting according to comprehensive cost analysis.

Emission of volatile organic compounds from a small-scale municipal solid waste transfer station: Ozone-formation potential and health risk assessment

Volatile organic compounds (VOCs) are the main precursors of tropospheric ozone and secondary aerosol generation, posing a threat to human health and affecting the environmental climate. A large quantity of VOCs can be produced in the initial decomposition stage of municipal solid waste (MSW). In this study, the atmosphere in an MSW transfer station was monitored for one year. The emission characteristics of VOCs in different seasons and working hours were analyzed, and the ozone-formation potential of VOCs was calculated through the maximum incremental reaction method, and health risks posed by the VOCs in the MSW transfer station were assessed. The results showed that the highest concentration of VOCs appeared in spring and summer, accounting for 70.6% and 26.6% of total VOCs (TVOCs) in peak working periods, respectively. Oxygenated compounds and terpenes contributed most to ozone formation, accounting for 41.0% and 50.6% of total ozone formation, respectively. The carcinogenic risks were above the safe threshold, labeled "probable risks". Tetrachloroethylene and 1,2-dichloroethane were the main contributors to carcinogenic risks. The mean non-carcinogenic risks were within the safe threshold in the MSW transfer station. From the perspective of protecting human health and ecological environmental safety, VOC control needs to be further strengthened in the transfer station.

Effect of source-classified and mixed collection from residential household waste bins on the emission characteristics of volatile organic compounds

The implementation of domestic waste classification following the principles of reduction, recycling, and harmlessness is an effective method to improve the urban and rural environments and to promote resource recycling. However, in many developing countries, the community residents lack awareness of the benefits of classified collection, which leads to a lack of initiative to classify MSW. To make the people realize the importance of MSW classification and increase the classification dynamics, Suzhou, China was taken as an example in this study, and residential areas were selected as sampling sites for classified and mixed collection of domestic waste. The main components of the odorous volatile organic compounds (VOCs) emitted from the dustbins via different disposal modes were determined by sampling in spring, summer, autumn, and winter. In addition, the ozone formation potential (OFP) and human health risk assessment of the VOCs were analyzed. Halogenated compounds were the major pollutants from the household waste dustbins of the residential areas. However, aromatic compounds contributed the most to the OFP of the VOCs. The OFP of VOCs reached the highest peak in summer, which was 1.02 × 10³ μg/m³. Furthermore, more attention needs to be paid in classifying waste to reduce the concentration of OFP. Although there was a carcinogenic risk in spring and summer, it declined after waste classification. Compared with mixed collection, the source-classified collection of garbage had advantages in terms of controlling the emission of VOCs, ozone formation potential, and human health risk. These results could provide the evidence demonstrating the advantages of waste classification and attract people's attention. Furthermore, the results can also provide impetus to those countries, where separate collection of waste has not yet been implemented, to improve the enthusiasm for classification and the integrity of waste classification system. Residents should be encouraged to classify household waste in residential areas.

Emission characteristics and health risk assessment of VOCs from a food waste anaerobic digestion plant: A case study of Suzhou, China

The process of anaerobic digestion in food waste treatment plants generates a large amount of volatile organic compounds (VOCs). Long-term exposure to this exhaust gas can pose a threat to the health of workers and people living nearby. In this study, VOCs emitted from different working units in a food waste anaerobic digestion plant were monitored for a year. Variations in VOCs emitted from each unit were analyzed and a health risk assessment was conducted for each working unit. The results show that the concentration of VOCs in different units varied greatly. The highest cumulative concentration of VOCs appeared in the hydrothermal hydrolysis unit (3.49 × 10⁴ μg/m³), followed by the sorting/crushing room (8.97 × 10³ μg/m³), anaerobic digestion unit (6.21 × 10² μg/m³), and biogas production unit (2.01 × 10² μg/m³). Oxygenated compounds and terpenes were the major components of the emitted VOCs, accounting for more than 98% of total VOC emissions. The carcinogenic risk in the plant exceeded the safety threshold (ILCR<1 × 10^-6), while the non-carcinogenic risk was within the acceptable range (HI < 1). The carcinogenic risk from the hydrothermal hydrolysis unit was the highest, reaching 4.4 × 10^-5, and was labeled as "probable risk." The carcinogenic risk at the plant boundary was 1.2 × 10^-5, indicating exhaust gases can cause a health threat to neighbors. Therefore, management VOCs in anaerobic digestion plants should receive more attention, and employees should minimize the time they spend in the hydrothermal hydrolysis unit.

Preservation of nitrogen and sulfur and passivation of heavy metals during sewage sludge composting with KH2PO4 and FeSO4

Composting is an effective method for treating sewage sludge. The aim of this work was to study preservation of nitrogen and sulfur and passivation of heavy metals during sewage sludge composting with KH₂PO₄ and FeSO₄. The results show the loss rate of N decreased by 27.5% while that of S was increased by 32.1% compared with the control treatment during composting when KH₂PO₄ and FeSO₄ were added. X-ray absorption near-edge structure spectra show that S was converted to a highly oxidizable state during sewage sludge composting with added KH₂PO₄. The mobility factors of Cu, Zn, and Pb after composting were found to decrease by 13.6%, 21.6%, and 3.8%, respectively, compared with those before composting when KH₂PO₄ was added. Adding these two materials to Cu and Zn inhibits Zn₃(PO₄)₂(H₂O)₄ and Cu₅(PO₄)₂(OH)₄ from transforming into more mobile forms, while adding these materials to Pb promotes Pb₃(PO₄)₂ formation.

Removal of triclosan during wastewater treatment process and sewage sludge composting-A case study in the middle reaches of the Yellow River

Triclosan (TCS) is widely used as an antibacterial disinfectant in personal care products, especially in rapidly-urbanizing countries, such as China. Almost all TCS enters wastewater treatment plants (WWTPs), but the fate of the TCS in the WWTPs is unclear. TCS may be present in sewage sludge or in effluent, and the discharge of TCS into an ecosystem can pose environmental risks. In the present study, influent, effluent, and sewage sludge were collected from four typical urban WWTPs, and the fate of TCS in the plants was investigated. The study was conducted in Zhengzhou, a city in the middle reaches of the Yellow River in China. The sewage sludge was used for aerobic composting to study the influences of different ventilation treatments on the biodegradation effects of TCS and the changes in the microbial community during the composting process. The results showed that the mean concentration of TCS in the influent of the four typical WWTPs was 397.1 ng/L. The mean level of TCS in the effluent was 8.0 ng/L. The mean concentration of TCS in the sewage sludge was 814.4 ng/g. For the four WWTPs, the percentages of TCS removal were 97.6% (Nansanhuan), 97.6% (Xinzheng), 98.8% (Wulongkou), and 97.9% (Chenyu), respectively. The sewage sludge enrichment rates for TCS ranged between 36.4% and 49%. Therefore, there is a need to focus on the environmental risks from sewage sludge. During aerobic composting, the TCS was effectively degraded under three ventilation strategies. Thus, improved ventilation could enhance the degradation rate of TCS. Moreover, TCS degradation occurred in the mesophilic period and in the early stage of the thermophilic phase period. Finally, the degradation rates of TCS in sewage sludge samples composted with low-, medium-, and high-ventilation treatments were 48.1%, 59.0%, and 59.5%, respectively. Thus, high ventilation could provide enough oxygen for the pile and enhanced microorganism activity, benefiting the degradation of TCS. In addition, the microbial communities change during the composting process, and a diversity index of the changes can help explain the composting process.

Emission characteristics of VOCs and potential ozone formation from a full-scale sewage sludge composting plant

Volatile organic compounds (VOCs) are the major components of the odor emitted from sewage sludge composting plants and are generally associated with odorous nuisances and health risks. However, few studies have considered the potential ozone generation caused by VOCs emitted from sewage sludge composting plants. This study investigated the VOC emissions from a full-scale composting plant. Five major treatment units of the composting plant were chosen as the monitoring locations, including the dewatered room, dewatered sludge, blender room, fermentation workshop, and product units. The fermentation workshop units displayed the highest concentration of VOC emissions at 2595.7 ± 1367.3 μg.m^-3, followed by the blender room, product, dewatered sludge, and dewatered room units, whose emissions ranged from 142.2 ± 86.8 μg.m^-3 to 2107.6 ± 1045.6 μg.m^-3. The detected VOC families included oxygenated compounds, alkanes, alkenes, sulfide compounds, halogenated compounds, and aromatic compounds. Oxygenated compounds, particularly acetone, were the most abundant compounds in all samples. Principal component analysis revealed that the dewatered room and dewatered sludge units clustered closely, as indicated by their similar component emissions. The product units differed from the other sampling units, as their typical compounds were methanethiol, styrene, carbon disulfide, and hexane, all of which were the products of the latter stages of composting. Among the treatment units, the fermentation workshop units had the highest propylene equivalent (propy-equiv) concentration. Dimethyl disulfide and limonene were the major contributors. Limonene had the highest propy-equiv concentration, which contributed to the increased atmospheric reactivity and ozone formation potential in the surrounding air. To control the secondary environmental pollution caused by the VOC emissions during sewage sludge composting, the emission of limonene and dimethyl disulfide must be controlled from the blender room and fermentation workshop units.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS₂ and ZnCu(P₂O₇) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ± 11.8%, which was the highest among all treatments.

Application of ceramsite and activated alumina balls as recyclable bulking agents for sludge composting

Composting is a major sludge-treatment method and bulking agents are very important in sludge composting. In this study, ceramsite and activated alumina balls were chosen as recyclable bulking agents for sludge composting. Variations in the temperature, pH, electrical conductivity, organic matter, dissolved organic carbon, moisture content, and heavy metals were detected during composting with different bulking-agent treatments as well as differences in the germination index values. The results showed that both bulking agents could ensure the maturity of the compost; further, ceramsite treatment resulted in the best water removal efficiency. According to the sequential extraction procedure, both ceramsite and activated alumina balls could stabilize Cd but they also increased the mobility of Zn. After comparing the effects of different particle sizes of ceramsite on composting, 20 mm was determined to be the most optimal value. Additionally, the recovery rates of ceramsite and activated alumina balls were 96.9% and 99.9%, respectively.

Oxygen Monitoring Equipment for Sewage-Sludge Composting and Its Application to Aeration Optimization

Oxygen is an important parameter for organic-waste composting, and continuous control of the oxygen in a composting pile may be beneficial. The oxygen consumption rate can be used to measure the degree of biological oxidation and decomposition of organic matter. However, without having a real-time online device to monitor oxygen levels in the composting pile, the adjustment and optimization of the composting process cannot be directly implemented. In the present study, we researched and developed such a system, and then tested its stability, reliability, and characteristics. The test results showed that the equipment was accurate and stable, and produced good responses with good repeatability. The equilibrium time required to detect oxygen concentration in the composting pile was 50 s, and the response time for oxygen detection was less than 2 s. The equipment could monitor oxygen concentration online and in real time to optimize the aeration strategy for the compost depending on the concentration indicated by the oxygen-measuring equipment.

[Effect of Fertilizers on Cadmium Uptake and Accumulation by Sunflowers]

A pot experiment was conducted to assess the phytoextraction potential for cadmium (Cd) of three types of sunflowers (edible, ornamental, and oil sunflowers) and the effects of the application of N, NP, and NPK fertilizers on Cd uptake of the three plants using Cd-contaminated soils collected from northern China. The results showed that fertilization could significantly increase the biomass, aboveground Cd concentrations and accumulation of ornamental and oil sunflowers, and the effect of NPK fertilizer was significantly better than those of other treatments. Cd concentrations of the aboveground parts of edible, ornamental, and oil sunflowers were 6.89, 8.92, 6.97 mg·kg^-1, respectively. Fertilization treatment significantly improved the transport ability of Cd of the three types of sunflowers, and bioconcentration factors of edible, ornamental, and oil sunflowers were 2.63 (control) to 3.10 (NPK fertilizer), 2.80 (control) to 4.02 (NPK fertilizer), and 2.11 (control) to 3.14 (NPK fertilizer), respectively. The results further showed that the metal-enriched granules and cellular debris were the main enrichment sources in the subcellular fraction of the three types of sunflowers (more than 55%). In summary, sunflowers can be considered as plant material for remediation of Cd-contaminated soil. In addition, NPK fertilizers can effectively improve the efficiency of sunflowers.

Contamination of heavy metals and isotopic tracing of Pb in surface and profile soils in a polluted farmland from a typical karst area in southern China

Farmland top soils and soil profiles situated in the karst area of Guilin, Guangxi Zhuang Autonomous Region, southern China, reveal different degrees of heavy metal pollution, both in respect to the lateral as well as the vertical dimension. Pb isotope ratios clearly identify that heavy metal contributions to the soil represent the legacy of former Pb-Zn mining and smelting in the area. Depending upon soil properties, differences in the intensity of the vertical penetration of heavy metal pollution are discernible. Top soil coverage by local farmers provides little remediation. Consequently, hazardous conditions for the regional ecology, for agricultural usage and ultimately for human health remain in place. Based on chemical and isotopic results obtained, more effective remediation strategies need to be developed.

Emission characteristics and health risk assessment of volatile organic compounds produced during municipal solid waste composting

Municipal solid waste degradation during composting generates volatile organic compounds (VOCs), which can pose health risks the staff at the composting site and people living nearby. This problem restricts the widespread application of composting techniques. The characteristics of VOCs emitted from different units at a composting plant and the health risks posed were investigated in this study. A total of 44 VOCs (including alkanes, alkenes, aromatic compounds, halogenated compounds, oxygenated compounds, and sulfur-containing compounds) were identified and quantified. The highest VOC concentration (15484.1 ± 785.3 µg/m³) was found in primary fermentation, followed by the tipping unit (10302.1 ± 1334.8 µg/m³), composting product (4693.6 ± 1024.3 µg/m³), secondary fermentation (929.9 ± 105.2 µg/m³), and plant boundary (370.4 ± 75.8 µg/m³). The mean VOC concentration was 6356.0 µg/m³. The main compounds emitted during primary fermentation were oxygenated and those emitted from the tipping unit were alkenes. Health risk assessments indicate that VOCs did not pose unacceptable non-carcinogenic risks i.e., the HR values were <1 and carcinogenic risks (CR) values were <1.0 × 10^-4. These results indicate that VOC emissions do not pose health risks to the staff at the composting site or to people living nearby. However, the cumulative non-carcinogenic and carcinogenic risks posed by the VOC mixture were high, especially for the primary fermentation unit emissions. Therefore, protecting the staff working near the primary fermentation unit should be a priority. Measures should be taken to minimize cumulative non-carcinogenic and carcinogenic risks because people are exposed to a mixture of VOCs mixture rather than to a single type of VOC.

Biodegradation of nonylphenol during aerobic composting of sewage sludge under two intermittent aeration treatments in a full-scale plant

The urbanization and industrialization of cities around the coastal region of the Bohai Sea have produced large amounts of sewage sludge from sewage treatment plants. Research on the biodegradation of nonylphenol (NP) and the influencing factors of such biodegradation during sewage sludge composting is important to control pollution caused by land application of sewage sludge. The present study investigated the effect of aeration on NP biodegradation and the microbe community during aerobic composting under two intermittent aeration treatments in a full-scale plant of sewage sludge, sawdust, and returned compost at a ratio of 6:3:1. The results showed that 65% of NP was biodegraded and that Bacillus was the dominant bacterial species in the mesophilic phase. The amount of NP biodegraded in the mesophilic phase was 68.3%, which accounted for 64.6% of the total amount of biodegraded NP. The amount of NP biodegraded under high-volume aeration was 19.6% higher than that under low-volume aeration. Bacillus was dominant for 60.9% of the composting period under high-volume aeration, compared to 22.7% dominance under low-volume aeration. In the thermophilic phase, high-volume aeration promoted the biodegradation of NP and Bacillus remained the dominant bacterial species. In the cooling and stable phases, the contents of NP underwent insignificant change while different dominant bacteria were observed in the two treatments. NP was mostly biodegraded by Bacillus, and the rate of biodegradation was significantly correlated with the abundance of Bacillus (r = 0.63, p < 0.05). Under aeration, Bacillus remained the dominant bacteria, especially in the thermal phase; this phenomenon possibly increased the biodegradation efficiency of NP. High-volume aeration accelerated the activity and prolonged the survival of Bacillus. The risk of organic pollution could be decreased prior to sewage sludge reuse in soil by adjusting the ventilation strategies of aerobic compost measurements.

Heavy metal contents and enrichment characteristics of dominant plants in wasteland of the downstream of a lead-zinc mining area in Guangxi, Southwest China

A field investigation on the content of heavy metals in soils and 17 kinds of dominant plants from wasteland of the downstream of a Pb-Zn mine in Northwest Guangxi Zhuang Autonomous Region was carried out. The absorption and accumulation characteristics of heavy metals between plants and soil were compared, and the candidate species for ecosystem restoration of the area were selected. The results indicated that the soils had been subjected to pollution of heavy metals in varying degrees. The concentrations of Cd, Pb, Zn were 46.5, 57.3 and 23.7 times higher than their corresponding background values, respectively. The contents of Cd, Pb and Zn in the most analyzed plants exceed the normal ranges and the phytotoxic level. C. crepidioides, S. nigrum, B. pilosa, C. Canadensis, A. conyzoides, I. denticulata and E. crusgali showed strong capability in accumulation and transport of Cd, and they could be used as good candidates for Cd- phytoextraction. Among which, Cd concentration in the aerial part of C. crepidioides exceeded the threshold of Cd-hyperaccumulator. Thus, C. crepidioides demonstrated the basic characteristics of a Cd-hyperaccumulator. The lower translocation ratios for Cd, Cu, Zn and Pb in P. vittata and C. chinensis make them suitable for phytostabilization in the study area.

[Emission Characteristics and Ozone Formation Potential of VOCs from a Municipal Solid Waste Composting Plant]

In Beijing, the chemical composition and component concentrations of volatile organic compounds (VOCs) were investigated during the municipal solid waste composting process using a portable gas chromatograph coupled with a mass spectrometer. The contributions of VOCs to the ozone formation potential were computed using the maximum incremental reactivity (MIR) scale and the propylene-equivalent concentration scale. The results showed that the concentrations of waste discharge in the sorting room, the first fermentation workshop, the second fermentation workshop, the compost product workshop, and the plant boundary were 10302.1, 15484.1, 929.9, 4693.6 and 370.4 μg·m^-3, respectively. The main VOCs of the municipal solid waste composting plant were ethanol, limonene, and acetone. The propylene-equivalent concentrations of waste discharge in the sorting room, the first fermentation workshop, the second fermentation workshop, the compost product workshop, and the plant boundary were 25875.7, 4087.9, 378.0, 747.7 and 296.8 μg·m^-3, whereas the O₃ formation potentials computed using the MIR scale were 26979.3, 21168.3, 1469.3, 6439.6 and 455.8 μg·m^-3. Reducing pollution by controlling the VOCs emission of waste discharge in the sorting room and the first fermentation workshop is important and can decrease the ozone formation potential. Given the accuracy and accessibility of the method, the MIR scale is more suitable for calculating the ozone formation potential of VOCs emitted from the municipal solid waste composting plant.

Reduction in greenhouse gas emissions from sludge biodrying instead of heat drying combined with mono-incineration in China

Sludge is an important source of greenhouse gas (GHG) emissions, both in the form of direct process emissions and as a result of indirect carbon-derived energy consumption during processing. In this study, the carbon budgets of two sludge disposal processes at two well-known sludge disposal sites in China (for biodrying and heat-drying pretreatments, both followed by mono-incineration) were quantified and compared. Total GHG emissions from heat drying combined with mono-incineration was 0.1731 tCO₂e t^-1, while 0.0882 tCO₂e t^-1 was emitted from biodrying combined with mono-incineration. Based on these findings, a significant reduction (approximately 50%) in total GHG emissions was obtained by biodrying instead of heat drying prior to sludge incineration.

IMPLICATIONS

Sludge treatment results in direct and indirect greenhouse gas (GHG) emissions. Moisture reduction followed by incineration is commonly used to dispose of sludge in China; however, few studies have compared the effects of different drying pretreatment options on GHG emissions during such processes. Therefore, in this study, the carbon budgets of sludge incineration were analyzed and compared following different pretreatment drying technologies (biodrying and heat drying). The results indicate that biodrying combined with incineration generated approximately half of the GHG emissions compared to heat drying followed by incineration. Accordingly, biodrying may represent a more environment-friendly sludge pretreatment prior to incineration.

Odor composition analysis and odor indicator selection during sewage sludge composting

On the basis of total temperature increase, normal dehydration, and maturity, the odor compositions of surface and internal piles in a well-run sewage sludge compost plant were analyzed using gas chromatography-mass spectrometry with a liquid nitrogen cooling system and a portable odor detector. Approximately 80 types of substances were detected, including 2 volatile inorganic compounds, 4 sulfur organic compounds, 16 benzenes, 27 alkanes, 15 alkenes, and 19 halogenated compounds. Most pollutants were mainly produced in the mesophilic and pre-thermophilic periods. The sulfur volatile organic compounds contributed significantly to odor and should be controlled primarily. Treatment strategies should be based on the properties of sulfur organic compounds. Hydrogen sulfide, methyl mercaptan, dimethyl disulfide, dimethyl sulfide, ammonia, and carbon disulfide were selected as core indicators. Ammonia, hydrogen sulfide, carbon disulfide, dimethyl disulfide, methyl mercaptan, dimethylbenzene, phenylpropane, and isopentane were designated as concentration indicators. Benzene, m-xylene, p-xylene, dimethylbenzene, dichloromethane, toluene, chlorobenzene, trichloromethane, carbon tetrachloride, and ethylbenzene were selected as health indicators. According to the principle of odor pollution indicator selection, dimethyl disulfide was selected as an odor pollution indicator of sewage sludge composting. Monitoring dimethyl disulfide provides a highly scientific method for modeling and evaluating odor pollution from sewage sludge composting facilities.

IMPLICATIONS

Composting is one of the most important methods for sewage sludge treatment and improving the low organic matter content of many agricultural soils. However, odors are inevitably produced during the composting process. Understanding the production and emission patterns of odors is important for odor control and treatment. Core indicators, concentration indicators, and health indicators provide an index system to odor evaluation. An odor pollution indicator provides theoretical support for further modelling and evaluating odor pollution from sewage sludge composting facilities.

Interaction between sulfur and lead in toxicity, iron plaque formation and lead accumulation in rice plant

Human activities have resulted in lead and sulfur accumulation in paddy soils in parts of southern China. A combined soil-sand pot experiment was conducted to investigate the influence of S supply on iron plaque formation and Pb accumulation in rice (Oryza sativa L.) under two Pb levels (0 and 600 mg kg(-1)), combined with four S concentrations (0, 30, 60, and 120 mg kg(-1)). Results showed that S supply significantly decreased Pb accumulation in straw and grains of rice. This result may be attributed to the enhancement of Fe plaque formation, decrease of Pb availability in soil, and increase of reduced glutathione (GSH) in rice leaves. Moderate S supply (30 mg kg(-1)) significantly increased Fe plaque formation on the root surface and in the rhizosphere, whereas excessive S supply (60 and 120 mg kg(-1)) significantly decreased the amounts of iron plaque on the root surface. Sulfur supply significantly enhanced the GSH contents in leaves of rice plants under Pb treatment. With excessive S application, the rice root acted as a more effective barrier to Pb accumulation compared with iron plaque. Excessive S supply may result in a higher monosulfide toxicity and decreased iron plaque formation on the root surface during flooded conditions. However, excessive S supply could effectively decrease Pb availability in soils and reduce Pb accumulation in rice plants.

Impact of composting strategies on the degradation of nonylphenol in sewage sludge

Nonylphenol can be present in sewage sludge, and this can limit the use of the sewage sludge to amend soil. Composting is one of the most efficient and economical methods of making sewage sludge stable and harmless. The nonylphenol degradation rates during composting with added bulking agents and with aeration applied were studied. Three organic bulking agents (sawdust, corn stalk, and mushroom residue) were added to sewage sludge, and the effects of the bulking agents used and the amount added on nonylphenol degradation were determined. The highest apparent nonylphenol degradation rate (71.6%) was found for sewage sludge containing 20% mushroom residue. The lowest apparent nonylphenol degradation rate (22.5%) was found for sewage sludge containing 20% sawdust. The temperature of the composting pile of sewage sludge containing 20% sawdust became too high for nonylphenol to be efficiently degraded, and the apparent nonylphenol degradation rate was lower than was found for sewage sludge containing 10% sawdust. Increasing the ventilating time from 5 to 15 min increased the apparent nonylphenol degradation rate from 19.7 to 41.6%. Using appropriate aerobic conditions facilitates the degradation of nonylphenol in sewage sludge, decreasing the risks posed by sewage sludge applied to land. Adding too much of a bulking agent can decrease the amount of the nonylphenol degraded. Increasing the ventilating time and the amount of air supplied can increase the amount of nonylphenol degraded even if doing so causes the composting pile temperature to remain low.

Online monitoring of volatile organic compound production and emission during sewage sludge composting

The production and emission of volatile organic compounds (VOCs) were studied using an online monitoring method in a well-operated sludge composting plant. Results indicated that VOC production within the pile was different from emission at the pile surface. The total mass of VOC production was 1.09gCkgDM(-1), which was 2.3 times as high as the total mass of emission. The maximum production and emission masses occurred in the mesophilic phase of composting and were 444 and 202mgkgDM(-1)d(-1), respectively. VOC production and emission rates also varied rapidly at different times. The relationship of VOC production rates and time in an on/off aeration cycle at different periods could be expressed as a quadratic equation, while the emission rate could be expressed as a linear equation.

[Transformation of organic matter during thermophilic composting of pig manure]

Thermophilic composting of pig manure was studied in an attempt to elaborate upon organic matter transformation during the process and provided parameters for product maturity using chemical method. The following parameters were measured in 11 samples during the 42 days of composting: organic matter, dissolved organic carbon (DOC), degradable organic matter and humic matter (HM). Organic matter decreased during composting process constantly; DOC concentration increased to maximum at 10 days and declined thereafter; degradable organic matter decreased whole composting, but they increased in start of high-temperature stage; The increasing level of HM at various stages of composting indicate the progression of humification; H/F provide information correlating to conventional chemical parameters (organic matter, DOC) of compost maturity. Moreover, H/F has correlating to degradable organic matter and HM.

Changes of Cu, Zn, and Cd speciation in sewage sludge during connposting

The potential toxicity risks from heavy metals depend on their chemical speciation. The four stages of the Tessier sequential extraction method were employed to investigate changes in heavy metal speciation (Cu, Zn, and Cd) of sewage sludge during forced aeration composting, and then to identify whether the composting process would reduce or enhance their toxicities. Throughout the composting process, the exchangeable, carbonate-bound, Fe-Mn oxide-bound, and organic matter-bound fractions of Cu were converted to the residual Cu fraction. The organic matter-bound Cu fraction greatly contributed to this transformation. Residual Zn fraction was transformed to the Fe-Mn oxide-bound and organic matter-bound fractions after composting. The residual Zn fraction was a major contributor to the organic matter-bound Zn fraction. The availability of Cu and Zn was reduced by composting such that the risk of heavy metal toxicity decreased with prolonged treatment times. Additionally, attention should be paid to the increased availability of Cd in sewage sludge after composting treatment.

[Stratification of free air space and its dynamics in the process of co-composting]

Co-composting of sewage sludge and pig manure was studied. Free air space (FAS) in the whole composting pile was 26.2% at the temperature rising stage and 42.3% at the stage of high temperature composting. FAS in the upper portion of composting pile was higher than that in the lower, where the air was enough for microorganism to live on for two stages above. The FAS was 52.4% at the stage of the cooling, when the effect of stratification of FAS was significant. The FAS in the upper pile was bigger than that in the middle, which was bigger than that in the lower. At the stageof maturing, FAS was 54.7% and its stratified effect weakened, but the capability of aeration in the upper and in the middle of the pile was larger than that in the lower. At the different stages of composting, the degree of difference of FAS was of the order: the cooling stage > the high temperature stage > maturing stage > the temperature rising stage. The difference in the pile for every stage of composting was as follows: the upper > the middle > the lower. The change of FAS agreed with two-order kinetics.

[Stratification of volatile solid content and its dynamics in the process of co-composting]

Co-composting of sewage sludge and pig manure was conducted and it was indicated that, at the stages of temperature starting and high temperature composting, the difference of organic decomposition in the upper portion was largest among three portions of composting pile. The difference was largest in the lower part of the pile and the stratification effect of volatile solid (VS) content was formed at the stage of cooling, while it was largest in the middle and the stratification effect was still remarkable at the stage of maturity. At different stages of composting, the difference of VS content in the pile was of the order: the cooling > or = the maturity > the high temperature > the temperature starting. At each stage of composting, the difference of organic decomposition in the pile was as follows: the upper > the middle > the lower. The change of VS content met with first-order kinetics equation and decomposition rate of VS was 0.3 kg x d(-1) while average loss of VS content was 8.2% in the whole process of composting.