Effect of Common Pesticides Used in the Niger Delta Basin of Southern Nigeria on Soil Microbial Populations

The effects of eleven pesticides on the populations of bacteria, actinomycetes, fungi and protozoa was investigated by treating a garden soil with their recommended rates. The microbial populations were estimated using the standard plate-count technique. Of the ll pesticides investigated, phenylmercuric acetate (agrosan) at 50 g g^-1 inhibited bacterial density the most, i.e. from 4,600,000 to 220 cells g^-1. The pesticides were Pentachloronitrobenzene (PCNB), tetramethylmethylthiuram disulphide (thiram),1- naphthylmethylcarbamate (Vetox 85), 1,2,3,4,5,6-hexachlorocyclohexane (Gammalin 20), phenylmercuric acetate (Agrosan), tetrachloroterephthalic acid (Dacthal), 4-nitrophenyl –2-nitro-4-trifluoromethylphenyl ether (Preforan), 2-ethyl-6-methyl –N-2-methoxy –1-methyl ethyl-chloroacetanide (Dual), Benlate, Brestan and Gramoxone. Pentachloronitrobenzene (PCNB) at 240,000 g g^-1 reduced bacterial population from 4,600,000 to 2,100 cells g^-1, whereas tetramethylthiuram disulphide (thiram) at 100 g g^-1 suppressed it by 2 log orders of magnitude. Soil application of 1-naphthylmethylcarbamate (Vetox 85) at 100 g g^-1 and 1,2,3,4,5,6,-hexachlorocyclohexane (Gamalin 20) at 1,300 g g^-1 repressed the bacterial numbers by 2 log orders of magnitude each. Pentachloronitrobenzene reduced the actinomycetes density from 340,000 to 320 cells g^-1 and completely eliminated all fungal and protozoan propagules from the soil. The Gammalin 20 completely wiped out all the fungi, whereas phenylmercuric acetate totally eliminated all the protozoa and reduced the fungal population from 34,000 to 60 cells g^-1. In general, protozoa and fungi were more susceptible to fungicides than bacteria and actinomycetes. Pentachloronitrobenzene, 1,2,3,4,5,6,-hexachlorocyclohexane and phenylmercuric acetate were toxic particularly to soil microorganisms, whereas the herbicides dacthal, Preforan and Dual were quite harmless in soil at application rates of 0.1, 0.06 and 0.02 g g^-1 respectively.     

Allelochemicals and allelopathy from microorganisms in wheat rhizosphers

Allelochemicals from fungi and bacteria in wheat rhizosphere,as well as their allelopathic effects on wheat and maize have been conducted.Fungi and bacteria were incubated at temperature 28-30℃.The extracts were tested for bioassay.Some samples identified to be responsible for allelopathy have been determined by GC-MS.Some chemicals identified were selected to test again their bioactivity.The results showed that acidic extracts were more toxic to germination of wheat and maize seeds(statistic significant difference P<0.01 or P<0.05)and basic extracts were less toxic and stimulated effects on germination in some cases.A good relationship has been observed between the data of chemical analysis and bioassay. A wide variety of chemicals such as phenolic acids,organic acids,aldehydes,alcohol,ketones,nitrogen-containing chemicals,were identified by GC-MS.Some phenols and organic acids were identified to be inhibit and nitrogens-containing compounds were to be stimulate to germination of seeds and extension of root and shoot of wheat and maize.     

Long- and short-chain AHLs affect AOA and AOB microbial community composition and ammonia oxidation rate in activated sludge

Quorum sensing (QS) regulation of the composition of ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) communities and functions in wastewater treatment was investigated. Specifically, we explored the role of N-acyl-l-homoserine lactones (AHLs) in microbial community dynamics in activated sludge. On average, the specific ammonia-oxidising-rate increased from 1.6 to 2.8?mg?NH₄⁺-N/g?MLSS/hr after treatment with long-chain AHLs for 16?days, and the addition of AHLs to sludge resulted in an increased number of AOA/AOB amoA genes. Significant differences were observed in the AOA communities of control and AHL-treated cultures, but not the AOB community. Furthermore, the dominant functional AOA strains of the Crenarchaeota altered their ecological niche in response to AHL addition. These results provide evidence that AHLs play an important role in mediating AOA/AOB microbial community parameters and demonstrate the potential for application of QS to the regulation of nitrogen compound metabolism in wastewater treatment.     

Influence of carbon source and temperature on the denitrifying phosphorus removal process

To supply the valuable operating parameters for the popular usage of the new denitrifying phosphors removal process, it is essential to study the dominant biochemical reactions and the characteristics of denitrifying phosphorus removing bacteria (DPB). Thus, parallel batch experiments using DPB sludge were carried out to assess the effect of substrates (sewage, HAc, and endogenous carbon source) on denitrifying dephosphorus removal efficiency in this study. The results showed that the initial specific phosphorus release rate increased with the high concentration of the short-chain volatile fatty acids ratio in the influent, and sufficient phosphorus was released by DPB. This improved the subsequent denitrification and phosphorus uptake efficiency. The specific endogenous denitrification mainly relies on the internal carbon source (PHB) stored by poly-P bacteria. Denitrifying phosphorus removing bacteria were very hungry when the internal PHB was consumed. Consequently, the specific endogenous denitrification rate was low and the phosphorus uptake did not happen. On the other hand, in the experiment, the denitrifying phosphorus removal performance under two temperature conditions (8–10°C and 25–26°C) was also investigated and analyzed. It was found that the lower temperature decreased the specific phosphorus release and uptake rate, but did not inhibit the denitrifying phosphorus removal completely. Therefore, the negative influence of the low temperature on the overall phosphorus removal was not significant. Translated from Acta Scientiae Circumstantiae, 2006, 26 (2): 186–192 [译自: 环境科学学报]     

共基质条件下TNT降解菌的选育及其处理效果

选取SBR弹药销毁废水处理系统中的活性污泥作为菌源,在共基质条件下,经过驯化和筛选,分离出11株可降解TNT的单菌,从中选出生长速度较快的3株菌JT1,JT2,JT3进行了单菌及混菌降解能力测试,结果表明:混合菌JTH降解能力最强,其适宜环境条件为25℃～30℃,pH7.5～9.0,基质中添加2g/L葡萄糖可显著增强混菌JTH生长并可使24h内的TNT降解率达到96 1%;模拟废水的处理实验表明:混菌JTH对COD的去除率>80%,TNT降解率80%～90%;生物强化实验表明:以0.1的菌量污泥比在SBR系统中投加混合菌可使系统的出水COD稳定在100mg/L左右,出水TNT浓度<5mg/L。     

Microbial Fe(III) Reduction in Acidic Mining Lake Sediments after Addition of an Organic Substrate and Lime

To elucidate the role of Fe(III) reduction in mining lake sediments amended with organic substrates, we performed a large (10 m diameter) enclosure experiment in which sediments were amended with Carbokalk, a waste product from sugar industry containing organic carbon and lime. Fe(III) reduction rates were determined monthly by measuring the accumulation of Fe(II) in the sediments in the field. Fe(III) reduction rates were also determined by incubating sediment samples with synthetic Fe(III) oxyhydroxide under in situ temperature in the laboratory. Sulfate reduction was selectively inhibited in the Fe(III) reduction experiments by addition of sodium molybdate. Sulfate reduction was measured by accumulation of reduced inorganic sulfides in the field and by ³⁵S radiotracer using a core injection technique. Sediment incubation and determination of sulfate reduction rates with radiotracer showed that sulfate reduction and direct microbial Fe(III) reduction occured simultaneously in the upper centimeters of the sediments and that both processes contributed to alkalinity generation. However, Fe(III) reduction was the initial process and rates were at least 3.5 fold higher than sulfate reduction rates. The results indicate that the presence of suitable anions for Fe(II) precipitation as carbonate or sulfide is needed in order to prevent loss of potential alkalinity by Fe(II) diffusion and reoxidation in the water column.     

微生物法处理电镀废水技术概况与展望

微生物法处理电镀废水技术倍受关注，文章在介绍国内外微生物法处理电镀废水的试验研究和大规模工业生产的基础上，总结了微生物法处理电镀废水的机理、工艺流程，优点及存在问题，并指出了这一技术的研究热点和发展前景。     

Sterilization of Escherichia coli cells by the application of pulsed magnetic field

The inactivation of microorganisms by pulsed magnetic field was studied. It was improved that the application of electromagnetic pulses evidently causes a lethal effect on E. coil cells suspended in phosphate buffer solution Na2HPO4/NaH2 PO4 (0.334/0.867mmol/L). Experimental results indicated that the survivability( N/N0 ; where N0 and N are the number of cells survived per milliliter before and after electromagnetic pulses application, respectively) of E. coil decreased with magnetic field intensity B and treatment time t. It was also found that the medium temperatures, the frequencies of pulse f, and the initial bacterial cell concentrations have determinate influences in destruction of E. coil cells by the application of magnetic pulses. The application of an magnetic intensity B = 160 mT at pulses frequency f= 62 kHz and treatment time t = 16 h result in a considerable destruction levels of E. coil cells ( N/N0=10^-4). Possible mechanisms involved in sterilization of the magnetic field treatment were discussed. In order to shorten the treatment time, many groups of parallel inductive coil were used. The practicability test showed that the treatment time was shortened to 4 h with the application of three groups of parallel coil when the survivability of E. coli cells was less than 0.01%; and the power consumption was about 0.2 kWh/m^3 .     

Straw bio-degradation by acidogenic bacteria and composite fungi

A composite microbial system, including a strain of Candida tropicalis (W3), a strain of Lactobacillus plantarm(WY3) and three strains of basidiomycete pL104, pL113 and C33, was chosen to degrade com straw.The final pH was acid owing to the inoculation of acidogenic bacteria, and under this condition the composite fungi system could produce complex enzyme to destroy the compact structure of corn straw. The experimental results showed that the biomass of composite fungi could reach up to maximum when the pH value was 4.5. Through the bio-degradation by combining acidogenic bacteria with the composite fungi system, the cellulose, hemi-ceUulose and lignin degradation rates of corn straw powder were 26.36%, 43.30% and 26.96%, respectively. And the gross crude protein content increased 60.41%. This study provided the evidence for the feasibility of developing a composite microbial system with high capability of degrading straw lignocelluloses in order to make reasonable use of straw resource and protect rural eco-environment.     

海藻提取物对富营养化水体氮素循环影响研究

利用国外引进的海藻提取物EClean制剂对富营养化水体进行处理试验,经过定量测定处理和对照水体中氮循环细菌数量的变化,得出EClean制剂能够促进水体的氨化细菌、亚硝化细菌、硝化细菌的生长,并维持了曝气条件下一定数量的反硝化细菌,通过此处理使得在同一反应器中、同一条件下完成硝化作用和反硝化作用成为可能,加速了水体的氮素循环,使水体总氮下降明显。