土壤农用地膜微生物降解研究进展

地膜可保持土壤湿度,调节土壤温度及限制杂草生长从而促进农作物增产,在现代农业生产中具有不可或缺的作用.然而,地膜主要成分聚乙烯（PE）性质稳定,难以降解,极易在农田土壤中残留并积累.此外,地膜在生产过程中添加邻苯二甲酸酯类（PAEs）作为塑化剂,该类有机物极易在土壤和水体环境中积累和迁移,且生物毒性大,对生态环境、粮食安全和人体健康构成极大威胁.聚乙烯和邻苯二甲酸酯复合污染是土壤有机污染治理的重点和难点.因此,农用地膜污染土壤修复是环境科学研究的重要课题,亦是作物生产安全和人类健康的重要保障.微生物降解的生物修复较物理化学技术具有效率高、无二次污染、成本低、环境扰动小等优点,具有广泛应用前景.由此,本文综述农用地膜使用和土壤残留现状及其生物降解的研究进展,以期为地膜污染农田土壤的生物修复提供基础信息和技术参考.     

聚乙烯废塑料流化床裂解炉的设计

利用热裂解法可将废塑料制成液体燃料和化学品,其对保护环境及社会的可持续发展有重要意义。对废塑料的裂解油化现状及热裂解反应做了初步的研究,并确定了一种适合的工艺流程;通过设计计算确定了聚乙烯废塑料流化床裂解炉中影响裂解的主要性能参数,对裂解炉的结构设计过程做了较详细的阐述,为流化床反应器的设计提供参考。     

用正交设计法研究阻燃LDPE薄膜配方

以低密度聚乙烯LDPE、氢氧化镁和微胶囊化红磷为原材料,利用正交设计法研究了新型阻燃薄膜配方,制备了阻燃型低密度聚乙烯薄膜,并对其氧指数进行测试.结果表明,新型配方中的氢氧化镁和微胶囊化红磷具有协同阻燃效果,并能在一定程度上解决燃烧时的熔滴现象;当氢氧化镁添加量小于29%时,两种阻燃剂对体系阻燃性的影响差别不明显;与纯LDPE薄膜相比,阻燃LDPE薄膜由于添加了上述两种阻燃成分,体系氧指数提高4%,改善了阻燃效果.     

Best management practices for airport deicing stormwater

With the advent of new regulations concerning aircraft deicing and management of spent aircraft deicing fluids (ADFs), many airports now face the dual challenges of simultaneously maintaining public safety and protecting the environment. This paper provides a theoretical assessment of the potential environmental impact of stormwater runoff and offers detailed current information on alternative deicing fluid application methods and materials, collection and treatment practices.     

Bacterial degradation of a new polyester,polyethylene glycol-phthalate polyester

Microorganisms which can assimilate a new polyester synthesized from polyethylene glycol (PEG) as a dihydroxyl compound and phthalic acid as a dicarboxyl compound were isolated from soils by enrichment culture techniques. Two cultures, K and N, were obtained: Culture K grew on PEG 4000 polyester and culture N assimilated PEG 6000 polyester. Each culture included two bacteria indispensable for the degradation of polyesters: bacteria K1 and K2 for PEG 4000 polyester-utilizing culture K and bacteria N1 and N2 for PEG 6000 polyester-utilizing culture N. Bacteria K2 and N2 were responsible for the hydrolysis of ester bonds in a polyester and both were identified as the same species,Comamonas acidovorans. Bacteria K1 and N6 could assimilate PEG as a sole carbon and energy source. Both are Gram-negative, non-spore-forming rods and resembled each other on their colony characteristics, although strain K1 could not grow on PEG 6000.C. acidovorans N2 (K2) grew on dialkyl phthalates (C₂–C₄) and phthalate and tributyrin, but not on PEG, diphthalic PEG, and PEG phthalate polyesters. Their culture supernatant and washed cells hydrolyzed PEG (400–20,000) phthalate and sebacate polyesters.C. acidovorans had higher esterase activity toward PEG phthalate, isophthalate, and terephthalate polyesters than known esterase and lipases. The esterase seemed to be an extracellular one and attached to the cell surface.     

Increased biodegradation of a low-density polyethylene (LDPE) matrix in starch-filled LDPE materials

Preheated¹⁴C-labeled LDPE-films with 15% corn starch and a proxidant formulation [masterbatch (MB)] incubated in aqueous solutions with fungi at ambient temperature are about three times more susceptible to biodegradation than the corresponding preheated pure LDPE as observed by liquid scintillation counting (LSC). The inbuilt induction time before autoxidation commences can be shortened by initial heating. Preheated LDPE-MB materials biodegrade about five times faster than nonheated ones. After 1 year of biodegradation of nonheated LDPE-MB, sporadic increases in the evolution of¹⁴CO₂ have been noted, showing that the induction time may be running toward and end.     

Degradation of starch-plastic composites in a municipal solid waste landfill

The rate and extent of deterioration of starch-plastic composites were determined over a 2-year period for samples buried in a municipal solid waste landfill. The deterioration of the starch-plastic composites following exposure was determined by measuring changes in tensile properties, weight loss, and starch content of samples retrieved from the landfill. Elongation decreases of 92 and 44% were measured for starch-plastic composite LDPE and LLDPE films, respectively, while elongation decreases of 54 and 21% were measured for their corresponding control films following 2 years of burial. Starch loss of 25% for LLDPE and 33% for LDPE starch-plastic composite films was measured following 2 years of landfill burial. Starch-plastic composites did not fragment or lose mass during the 2-year landfill burial. The limited degradation observed for the starch-plastic composites was attributed to the ineffectiveness of the prooxidant additive to catalyze the thermal oxidation of the polyethylene or polypropylene component of the starch-plastic composite under the environmental conditions present within the landfill.     

The influence of soil macroinvertebrates on primary biodegradation of starch-containing polyethylene films

The primary biodegradability of polyethylene (PE) films containing different percentages of cornstarch (0–50%) and other additives (prooxidant, oxidized polyethylene) was tested using four species of earthworms (Eisenia fetida, Lumbricus terrestris, Aporectodea trapezoides, Aporectodea tuberculata), three species of cockroaches (Periplaneta americana, Blaberus sp.,Blattella germanica), termites (Reticulotermes flavipes), sowbugs (Porcellio laevis), and crickets (Acheta domesticus). These studies were conducted to elucidate the potential role of soil macroinvertebrates in degrading starch/PE biodegradable plastics. The results of the macroinvertebrate bioassays indicate that crickets, cockroaches, and sowbugs consumed starch-containing PE films most readily. In addition, the degree to which the films were attacked and consumed was directly related to the starch content of the film. Films with oxidized polyethylene and those containing prooxidant (vegetable oil and a transition metal catalyst) were also consumed. None of the four species of earthworms tested or the termites showed any activity toward the starch/polyethylene films. These results have important implications for determining the fate of novel plastic formulations which claim to be biodegradable in natural environments. Studies such as these, coupled with studies on microbial degradation, will help provide the type of information needed to assess the environmental fate of biodegradable starch/PE plastics and fill the voids in the scientific database regarding this rapidly developing field.     

Starch-filled polyethylene in a composting environment: Evidence for polyethylene matrix oxidation

Two series of starch-filled polyethylene films, consisting of high-density or low-density polyethylene and 0–20% starch, have been exposed for 60 days to a controlled composting environment. Evidence is reported that the oxidation of the polyethylene matrix is dependent upon the polyethylene type and content of starch.     

An accelerated laboratory study evaluating the disintegration rates of plastic films in simulated aquatic environments

Six plastic films were exposed to accelerated sunlight while in simulated aquatic environments to determine the effects of chemical composition and environment on the disintegration rates. An environment of UV light/no water was used as a control to determine if the microorganisms in the aquatic systems enhanced the breakdown of the plastic films. The disintegration rate of the plastics was determined by monitoring changes in selected physical properties. The plastics included two conventional plastics commonly used in packaging (LDPE and polystyrene) and four plastics enhanced to have more rapid breakdown in the environment (2% ECO, 10% ECO, PE with ketone graft, and PE with starch). The two ECO copolymers had a significantly faster loss of physical properties than the other plastics evaluated in this study. Degradation was influenced by environmental conditions. Those plastics that showed a change in physical properties had a greater change faster in the UV light/no water than in the environments where water was present. Plastics on the surface of the water showed a more rapid loss of properties than those samples partially or completely submerged. This can be attributed to decreased light intensity and the lack of heat buildup.