[Applications of biofilm in environmental pollution control and the related challenges]. / 生物膜在环境污染治理中的应用及挑战.

Biofilm has been used in environmental pollution control in recent years due to its characteristics of adsorption and biodegradation. Beyond the success of its utilization in wastewater treatment, biofilm technique has high application value in the remediation of heavy metals and organic pollutants in soils. With the extensive attention and research of emerging pollutants such as microplastics and antibiotic resistance genes (ARGs), the pivotal role of biofilm can not be overlooked. Here, we presented a comprehensive review of the structure, formation mecha-nism, population, and functional aspects of biofilm, as well as its applications and mechanisms in environmental pollution control in recent years. We emphatically discussed the removal mechanism and application progress of biofilm on heavy metals and organic pollutants. We further expounded some novel environmental challenges posed by biofilm under new circumstances, including the coexistence of various pollutants in plastisphere, the spread of ARGs, and the accumulation of pathogens. Finally, we put forward the gaps of current research and prospects for future research, especially the importance of exploring the interaction relationship and mechanism between biofilm and various pollutants. It is expected to provide theoretical basis for the development of new technology of biofilm remediation.

Effect of migration and transformation of iron on the endogenous reduction of H2S in anaerobic landfill.

Hydrogen sulfide (H2S) is a major odor in landfill gas and needs urgent treatment. In this study, the effect of migration and transformation of iron on the endogenous reduction of H2S was investigated in two simulated landfills. The results showed that the H2S emission concentration from the landfill cover of conventional anaerobic landfill (CL) and anaerobic landfill with leachate recirculation (RL) could reach 19.4mgm(-3) and 24.1mgm(-3), respectively. However, the migration and transformation of iron in anaerobic landfill with different operational modes results in different endogenous reduction mechanism for H2S. The proportion of precipitation-reduction mechanism and oxidation-reduction mechanism in CL was 73.3% and 26.3%, respectively. But for RL, the function of oxidation was enhanced, and the sulfide content was reduced 23.1% compared with CL. The iron in landfill with leachate recirculation revealed good endogenous reduction effect on H2S control after a period of time landfilling.

Characteristics of H2S emission from aged refuse after excavation exposure.

Hydrogen sulfide (H2S(g)) emission from landfills is a widespread problem, especially when aged refuse is excavated. H2S(g) emission from aged refuse exposed to air was investigated and the results showed that large amounts of H2S(g) can be released, especially in the first few hours after excavation, when H2S(g) concentrations in air near refuse could reach 2.00 mg m(-3). Initial exposure to air did not inhibit the emission of H2S(g), as is generally assumed, but actually promoted it. The amounts of H2S(g) emitted in the first 2 d after excavation can be very dangerous, and the risks associated with the emission of H2S(g) could decrease significantly with time. Unlike a large number of sulfide existed under anaerobic conditions, the sulfide in aged municipal solid waste can be oxidized chemically to elemental sulfur (but not sulfate) under aerobic conditions, and its conversion rate was higher than 80%. Only microorganisms can oxidize the reduced sulfur species to sulfate, and the conversion rate could reach about 50%. Using appropriate techniques to enhance these chemical and biological transformations could allow the potential health risks caused by H2S(g) after refuse excavation to be largely avoided.

Water state changes during the composting of kitchen waste.

Changes in water states during the composting of kitchen waste were determined. Three experiments, R(55), R(60), and R(65), with different initial moisture contents, 55%, 60%, and 65%, respectively, were performed. Three water states, entrapped water (EW), capillary water (CW), and multiple-molecular-layer water (MMLW), were monitored during the experiments. Changes only occurred with the EW and CW during the composting process. The percentage of EW increased, and the percentage of CW decreased as the composting process progressed. The R(60) experiment performed better than the other experiments according to changes in the temperature and carbon-to-nitrogen ratio (C/N). The percentage of EW correlated well (P<0.05) with the dissolved organic carbon content (DOC), electrical conductivity (EC), pH, and C/N, and was affected by the hemicellulose and cellulose contents.

Sulfide oxidation and nitrate reduction for potential mitigation of H2S in landfills.

Because H2S emitted by landfill sites has seriously endangered human health, its removal is urgent. H2S removal by use of an autotrophic denitrification landfill biocover has been reported. In this process, nitrate-reducing and sulfide-oxidizing bacteria use a reduced sulfur source as electron donor when reducing nitrate to nitrogen gas and oxidizing sulfur compounds to sulfate. The research presented here was performed to investigate the possibility of endogenous mitigation of H2S by autotrophic denitrification of landfill waste. The sulfide oxidation bioprocess accompanied by nitrate reduction was observed in batch tests inoculated with mineralized refuse from a landfill site. Repeated supply of nitrate resulted in rapid oxidation of the sulfide, indicating that, to a substantial extent, the bioprocess may be driven by functional microbes. This bioprocess can be realized under conditions suitable for the autotrophic metabolic process, because the process occurred without addition of acetate. H2S emissions from landfill sites would be substantially reduced if this bioprocess was introduced.

Bioaccessibility and health risk of heavy metals in ash from the incineration of different e-waste residues.

Ash from incinerated e-waste dismantling residues (EDR) may cause significant health risks to people through ingestion, inhalation, and dermal contact exposure pathways. Ashes of four classified e-waste types generated by an incineration plant in Zhejiang, China were collected. Total contents and the bioaccessibilities of Cd, Cu, Ni, Pb, and Zn in ashes were measured to provide crucial information to evaluate the health risks for incinerator workers and children living in vicinity. Compared to raw e-waste in mixture, ash was metal-enriched by category incinerated. However, the physiologically based extraction test (PBET) indicates the bioaccessibilities of Ni, Pb, and Zn were less than 50 %. Obviously, bioaccessibilities need to be considered in noncancer risk estimate. Total and PBET-extractable contents of metal, except for Pb, were significantly correlated with the pH of the ash. Noncancer risks of ash from different incinerator parts decreased in the order bag filter ash (BFA) > cyclone separator ash (CFA) > bottom ash (BA). The hazard quotient for exposure to ash were decreased as ingestion > dermal contact > inhalation. Pb in ingested ash dominated (>80 %) noncancer risks, and children had high chronic risks from Pb (hazard index >10). Carcinogenic risks from exposure to ash were under the acceptable level (<10(-6)) both for children and workers. Exposure to ash increased workers' cancer risks and children's noncancer risks. Given the risk estimate is complex including toxicity/bioaccessibility of metals, the ways of exposure, and many uncertainties, further researches are required before any definite decisions on mitigating health risks caused by exposure to EDR incinerated ash are made.

Effects of added polyacrylamide on changes in water states during the composting of kitchen waste.

The effects of adding polyacrylamide (PAM), to attempt to delay the loss of capillary water and achieve a better level of organic matter humification, in the composting of kitchen waste were evaluated. Four treatments, with initial moisture content of 60 % were used: 0.1 % PAM added before the start of composting (R1), 0.1 % PAM added when the thermophilic phase of composting became stable (at >50 °C) (R2), 0.1 % PAM added when the moisture content significantly decreased (R3), and no PAM added (R4). The introduction of PAM in R1 and R2 significantly increased the capillary force and delayed the loss of moisture content and capillary water. The introduction of PAM in R2 and R3 improved the composting process, in terms of the degradation of biochemical fractions and the humification degree. These results show that the optimal time for adding PAM was the initial stage of the thermophilic phase.

Reduction of heavy metals in residues from the dismantling of waste electrical and electronic equipment before incineration.

Residues disposal from the dismantling of waste electrical and electronic equipment are challenging because of the large waste volumes, degradation-resistance, low density and high heavy metal content. Incineration is advantageous for treating these residues but high heavy metal contents may exist in incinerator input and output streams. We have developed and studied a specialized heavy metal reduction process, which includes sieving and washing for treating residues before incineration. The preferable screen aperture for sieving was found to be 2.36mm (8 meshes) in this study; using this screen aperture resulted in the removal of approximately 47.2% Cu, 65.9% Zn, 26.5% Pb, 55.4% Ni and 58.8% Cd from the residues. Subsequent washing further reduces the heavy metal content in the residues larger than 2.36mm, with preferable conditions being 400rpm rotation speed, 5min washing duration and liquid-to-solid ratio of 25:1. The highest cumulative removal efficiencies of Cu, Zn, Pb, Ni and Cd after sieving and washing reached 81.1%, 61.4%, 75.8%, 97.2% and 72.7%, respectively. The combined sieving and washing process is environmentally friendly, can be used for the removal of heavy metals from the residues and has benefits in terms of heavy metal recycling.

Sorption behavior of dibutyl phthalate and dioctyl phthalate by aged refuse.

Sorption is a fundamental process controlling the transformation, fate, degradation, and biological activity of hydrophobic organic contaminants in the environment. We investigated the kinetics, isotherms, and potential mechanisms for the sorption of two phthalic acid esters (PAEs), dibutyl phthalate (DBP) and dioctyl phthalate (DOP), on aged refuse. A two-compartment first-order model performed better than a one-compartment first-order model in describing the kinetic sorption of PAEs, with a fast sorption process dominating. Both the Freundlich and Dubinin-Astakhov (DA) models fit the sorption isotherms of DBP and DOP, with the DA model being of a better fit over the range of apparent equilibrium concentrations. The values of the fitting parameters (n, b, E) of the PAEs suggest nonlinear sorption characteristics. Higher predicted partition coefficient values and saturated sorption capacity existed in refuse containing larger quantities of organic matter. The sorption capacity of DOP was significantly higher than that of DBP. PAE sorption was dependent on liquid phase pH. Desorption hysteresis occurred in PAE desorption experiments, especially for the long-chain DOP. PAEs may therefore be a potential environmental risk in landfill.

Role of iron in H(2)S emission behavior during the decomposition of biodegradable substrates in landfill.

Hydrogen sulfide (H2S) is regarded as a major odor causing compound in landfill gas that may lead to adverse environmental and health effects. In this study, the potential role of iron in the entire life cycle of H2S production and emission was investigated during the decomposition of biodegradable substrates in the landfilled refuse. The results showed that the quantity of H2S emission decreased about 95% when Fe(OH)3 was present in the biodegradable sulfur-containing substrates. During this degradation process, a lot of sulfide was generated, which was present mostly as ferrous sulfide. In addition, a total of 7.68% S-H2S of total sulfur released as gas phase could be remained in solid-liquid phase effectively in the simulated substrates with iron. Thus, using the appropriate way to take advantage of iron "hidden" in the landfilled refuse might be a good choice for in situ control of H2S emission. Moreover, if this high level of iron is not presented, landfill odor pollution might become more serious.

Effects of ammonia on methane oxidation in landfill cover materials.

The effects of ammonia (NH3) on CH4 attenuation in landfill cover materials consisting of landfill cover soil (LCS) and aged municipal solid waste (AMSW), at different CH4 concentrations, were investigated. The CH4 oxidation capacities of LCS and AMSW were found to be significantly affected by the CH4 concentration. The maximum oxidation rates for LCS and AMSW were obtained at CH4 concentrations of 5% and 20%(v/v), respectively, within 20 days. CH4 biological oxidation in AMSW was significantly inhibited by NH3 at low CH4 concentrations (5%, v/v) but highly stimulated at high levels (20% and 50%, v/v). Oxidation in LCS was stimulated by NH3 at all CH4 concentrations due to the higher conversion of the nitrogen in NH3 in AMSW than in LCS. NH3 increases CH4 oxidation in landfill cover materials.

Enhanced reductive dechlorination of polychlorinated biphenyl-contaminated soil by in-vessel anaerobic composting with zero-valent iron.

Anaerobic dechlorination is an effective degradation pathway for higher chlorinated polychlorinated biphenyls (PCBs). The enhanced reductive dechlorination of PCB-contaminated soil by anaerobic composting with zero-valent iron (ZVI) was studied, and preliminary reasons for the enhanced reductive dechlorination with ZVI were investigated. The results show that the addition of nanoscale ZVI can enhance dechlorination during in-vessel anaerobic composting. After 140 days, the average number of removed Cl per biphenyl with 10 mg g(-1) of added nanoscale ZVI was 0.63, enhancing the dechlorination by 34 % and improving the initial dechlorination speed. The ZVI enhances dechlorination by providing a suitable acid base environment, reducing volatile fatty acid inhibition and stimulating the microorganisms. The C/N ratios for treatments with the highest rate of ZVI addition were smaller than for the control, indicating that ZVI addition can promote compost maturity.

Flow analysis of heavy metals in a pilot-scale incinerator for residues from waste electrical and electronic equipment dismantling.

The large amount of residues generated from dismantling waste electrical and electronic equipment (WEEE) results in a considerable environmental burden. We used material flow analysis to investigate heavy metal behavior in an incineration plant in China used exclusively to incinerate residues from WEEE dismantling. The heavy metals tested were enriched in the bottom and fly ashes after incineration. However, the contents of heavy metals in the bottom ash, fly ash and exhaust gas do not have a significant correlation with that of the input waste. The evaporation and recondensation behavior of heavy metals caused their contents to differ with air pollution control equipment because of the temperature difference during gas venting. Among the heavy metals tested, Cd had the strongest tendency to transfer during incineration (TCd=69.5%) because it had the lowest melting point, followed by Cu, Ni, Pb and Zn. The exchangeable and residual fractions of heavy metals increased substantially in the incineration products compared with that of the input residues. Although the mass of residues from WEEE dismantling can be reduced by 70% by incineration, the safe disposal of the metal-enriched bottom and fly ashes is still required.

Dechlorination of polychlorinated biphenyl-contaminated soil via anaerobic composting with pig manure.

Anaerobic dechlorination is an effective degradation pathway of higher chlorinated polychlorinated biphenyls (PCBs). The efficiency of anaerobic composting remediation of PCB-contaminated soil using pig manure was determined. The results show that the dechlorination of PCB-contaminated soil via anaerobic composting with pig manure is feasible. PCB concentration is the most critical factor. Elevated PCB concentrations can inhibit dechlorination but does not disrupt the anaerobic fermentation process. At 1 mg kg(-1) PCBs, the degradation rate of five or more chlorinated biphenyls is 43.8%. The highest dechlorination performance in this experiment was obtained when the soil-to-organic waste ratio, carbon-to-nitrogen ratio, moisture content, and PCB concentration were 2:3, 20, 60%, and 1 mg kg(-1), respectively.

Characterization of residues from dismantled imported wastes.

Residues from the imported wastes dismantling process create a great burden on the ambient environment. To develop appropriate strategies for the disposal of such residues, their characteristics were studied through background value analysis and toxicity leaching tests. Our results showed that the heavy metals concentrations in residues were high, particularly those of Cu (7180 mg kg(-1)), Zn (2783 mg kg(-1)), and Pb (1954 mg kg(-1)). Toxicity leaching tests revealed a high metal releasing risk of such residues if they are disposed of in a landfill. However, the residues of imported wastes were also found to have some intrinsic metal recycling value.

Co-digestion of kitchen waste and fruit-vegetable waste by two-phase anaerobic digestion.

The high salinity and fat contents of kitchen waste (KW) inhibits the effect of two-phase anaerobic digestion system. This research introduces fruit-vegetable waste (FVW) to alleviate the inhibition effect caused by salinity and fat concentrations, and tries to achieve an optimal addition ratio of FVW, an optimal hydraulic remain time (HRT) of acidogenic-phase reactor and methanogenic-phase reactor. A two-phase anaerobic digestion (AD) system was developed to co-dispose KW and FVW. Four sets of experiments were run with different mass proportions between KW and FVW (25-75, 50-50, 75-25, and 100-0% m/m). Considering the biodegradation rate and the acidification degree, the system with 25% KW had the best performance during the acidogenic phase. When the system was run with 50% KW, it not only had the best stability performance but also had a bigger capacity to treat KW than the system with 25% KW. The system with 50% KW was the best ratio in this two-phase AD system. Co-digestion of KW and FVW by two-phase AD is feasible. The addition of FVW can reduce the inhibition effect caused by salinity and fat concentrations, reduce the HRT, and lead to a higher degree of acidification.

Effect of deposit age on adsorption and desorption behaviors of ammonia nitrogen on municipal solid waste.

Ammonia nitrogen pollution control is an urgent issue of landfill. This research aims to select an optimal refuse for ammonia nitrogen removal in landfill from the point of view of adsorption and desorption behavior. MSW (municipal solid waste) samples which deposit ages were in the range of 5 to 15 years (named as R(15), R(11), R(7), and R(5)) were collected from real landfill site. The ammonia nitrogen adsorption behaviors of MSW including equilibrium time, adsorption isotherms, and desorption behaviors including equilibrium time were determined. Furthermore, the effects of pH, OM, Cu(II), Zn(II), and Pb(II) on adsorption and desorption behavior of ammonia nitrogen were conducted by orthogonal experiment. The equilibrium time of ammonia nitrogen adsorption by each tested MSW was very short, i.e., 20 min, whereas desorption process needed 24 h and the ammonia nitrogen released from refuses was much lesser than that adsorbed, i.e., accounted for 3.20 % (R(15)), 14.32 % (R(11)), 20.59 % (R(7)), and 20.50 % (R(5)) of each adsorption quantity, respectively. The maximum adsorption capacity estimated from Langmuir isotherm appeared in R(15)-KCl, i.e., 25,000 mg kg(-1). The best condition for ammonia nitrogen removal from leachate was pH >7.5, OM 23.58 %, Cu(II) <5 mg L(-1), Zn(II) <10 mg L(-1), and Pb(II) <1 mg L(-1). Ammonia nitrogen in landfill leachate could be quickly and largely absorbed by MSW but slowly and infrequently released. The refuse deposited for 15 years could be a suitable material for ammonia nitrogen removal.

Prevalence and related factors of injury caused by agricultural machinery in the 3 provinces Shandong, Henan and Hebei of China / 中华预防医学杂志

<p><b>OBJECTIVE</b>To study the prevalent characteristics and related factors of injuries caused by agricultural machinery in 3 provinces Shandong, Henan and Hebei in China.</p><p><b>METHODS</b>A total of 1621 agricultural machinery operators aged between 18 and 60 years old from Shandong, Henan and Hebei provinces were selected by purposive-cluster sampling method in 2009. Demographic characteristics, injury history caused by agricultural machinery in the last year and the related social and psychological factors were collected by self-designed questionnaire. We used statistical description to report the injury prevalence, and adopted the univariate and multivariate analysis to explore the risk factors.</p><p><b>RESULTS</b>The average incidence of injuries caused by agricultural machinery was 13.44% (213/1585) in the three provinces, of which 14.46% (202/1397) in males and 5.85% (11/188) in females (χ(2) = 10.56, P < 0.01). Most of injuries (155 cases, 72.77%) occurred between April and August. Being stuck by rolling starting handles (45 cases, 21.13%), being crushed by running or dropping machineries (32 cases, 15.02%), fall from machines (28 cases, 13.15%) ranked the top three causes of injuries. The main related machines were tractors and motor tricycles (133 cases, 62.44%). The leading types of injuries were scratch (115 cases, 53.99%), strain (68 cases, 31.92%) and fracture (37 cases, 17.37%).</p><p><b>RESULTS</b>of multivariate logistic regression analysis showed that being male (OR = 3.18, 95%CI:1.65-6.15), educational level above high school(OR = 1.69, 95%CI:1.21-2.34), annual family income <2000 yuan (OR = 1.94, 95%CI:1.13-3.32), operating experience ≤ 5 years (OR = 1.70, 95%CI:1.13-2.55), daytime sleepiness (OR = 2.89, 95%CI:1.66-5.01), smoking during machinery operation (OR = 1.43, 95%CI:1.05-1.96), bearing debts (OR = 1.88, 95%CI:1.35-2.63) and suffering from other diseases (OR = 1.42, 95%CI:1.02-1.98) were risk factors of agricultural machinery injuries.</p><p><b>CONCLUSION</b>The average incidence of injuries caused by agricultural machinery in the three provinces Shandong, Henan and Hebei, was rather high among agricultural machinery operators, especially in the males. Agricultural machinery injury has been an important issue endangering the health of rural labor force in recent years.</p>

[Transformation of dibutyl phthalate in bioreactor landfill].

Considering the refuse and leachate as one whole system, a conventional landfill (CL) was set as a control, transformation of dibutyl phthalate (DBP) in recirculated landfill (RL) and bioreactor landfill (BL) was studied. Results showed that DBP was detected in both leachate and refuse from CL, RL and BL. The initial DBP amount was 18.5 microg x g(-1) in the landfill refuse. In addition, the stabilization process of landfill, with sequences of BL > RL > CL, played an important role on the biodegradation of DBP in refuse. Compared to the acidic environment, the methanogenic environment was beneficial for DBP degradation. At the day of 310, refuse sedimentation rates were 7.0%, 11.9% and 24.3% in CL, RL and BL, respectively. DBP residual amounts were 2.1, 1.3 and 0.8 microg x g(-1), and its removal rates were 89.5%, 93.9% and 96.6% in the refuse from CL, RL and BL, respectively. The residual amounts of DBP with significant differences well fitted exponential decay models in CL, RL and BL. Finally, DBP biodegradation was obviously accelerated with the operation of leachate recirculation compared to the conventional operation, and it was further promoted with the introduction of methanogenic reactor.

Can Chlorella pyrenoidosa be a bioindicator for hazardous solid waste detoxification?

Four kinds of solid waste residue (SWR, S1 to S4) from different stages in a sequential detoxification process were chosen. The biotoxicity of the leachates from S1 to S4 was tested by Chlorella pyrenoidosa. The growth inhibition, the chlorophyll a (chla) and chlorophyll b (chlb) concentrations, and the ultrastructural morphology of cells of C. pyrenoidosa were studied. It shows that the growth inhibition of C. pyrenoidosa significantly increased with increasing leachate concentration when exposed to the leachates from S1, S2, S3, and S4, respectively. It well reflects the toxicity difference of leachate from SWR at different treatment stages, namely S1>S2>S3>S4. Correspondingly, the chla and chlb concentrations of C. pyrenoidosa increased gradually as SWR was treated deeply. Leachate disrupted chlorophyll synthesis and inhibited cell growth. The changing of the ultrastructural morphology of cells under different leachate exposures, such as volume of chloroplasts and quantity of thylakoids reducing, confirmed the toxicity decrease of leachates from different stages. C. pyrenoidosa is a good bioindicator for hazardous solid waste detoxification. The EC(50) at difference scenarios also suggests that it was feasible to estimate ecological toxicity of leachates to C. pyrenoidosa after exposure times of 72h. C. pyrenoidosa can be introduced to evaluate the effect of hazardous solid waste disposal by biotoxicity assessment.