Cleaning Technologies And Mechanisms Of River Water Polluted With N,N-dimethylformamide By Aquatic Plant-microbe Systems

N,N-dimethylformamide is an excellent organic solvent with stable chemical property. As it is miscible with both water and most organic solvents, DMF is extensively used in chemical industries such as petrochemical and pharmaceutical industries and in the production of leather and pesticides. Consequently, it is commonly found in high concentrations in many industrial effluents even after its recovery. River pollution resulted from the discharge of poorly treated wastewater with high concentration of DMF adversely affected the aquatic ecosystem and subsequently posed a threat to human health. In order to discuss the mechanism of the aquatic plant-microbe system used in the remediation of the Beishan River, Yutian River and Shangzhuang River in Wenzhou, China, which were polluted by DMF, and subsequently provide theoretical basis for optimization and application of the system, an Eco-tank of 10m, containing microbe and four aquatic plants was constructed to simulate the natural river. The purification performance of the Eco-tank system for DMF polluted river water, the physiological and biochemical changes of aquatic plants used in the system under the stress of DMF, the degradation mechanism of DMF, isolation of strain capable of degrading DMF, and the utilization of aquatic plants debris were investigated. The main results and conclusions obtained were as follows:1. The Eco-tank system was observed to remove DMF, chemical oxygen demand(COD) and ammonium nitrogen(NH4+ -N) efficiently. Removal of DMF was completely finished in tank 1 and 2 as the influent DMF was 75.42-161.05mg·L-1 under hydraulic retention time(HRT) of 10d,7d, and 5d, and DMF removal efficiencies in tank 1 were 91.7%,85.4% and 68.3%, respectively. The total organic carbon(TOC) decreased gradually through the tanks, and average removal efficiencies of TOC were 72.2%、64.7% and 63.0%, separately, with influent TOC concentration of 36.26-79.55mg·L-1 under HRT of 10d,7d, and 5d. The effluent COD was 8.0-44.8mg·L-1,with average value of 23.5mg·L-1, reaching the class V standard of environmental quality standards for surface water(GB3838-2002).2. The NH4+ -N presented rising tendency then followed by decreasing, and the effluent concentration of tank 1 was 9.81-28.53mg·L-1. When the HRT was 10d,7d, and 5d, average effluent NH4+ -N and total nitrogen(TN) were 2.58,3.41,5.85,4.74,5.92 and 8.47mg·L-1, respectively. Nitrate nitrogen(NO3- -N) and nitrite nitrogen(NO2- -N) were observed to be as lower than 0.5mg·L-1, indicating NH4+ -N was probably removed via absorption by aquatic plants. The aeration could improve the removal of NH4+ -N significantly, and average effluent NH4+ -N decreased to 0.89mg·L-1,84.8% lower than that without aeration, which met the class III standard of environmental quality standards for surface water. However, the removal of TN was not enhanced. The average effluent TN declined to 4.58mg·L-1 with the removal efficiency of 76.7% after inoculation with denitrification bacteria using bamboo fibre packing, which increased by 35.0% compared with that before inoculation.3. DMF could improve the growth of A. philoxeroides, while did not affect the growth of H. verticillata significantly. Low concentration of DMF(DMF≤400mg·L-1) could enhance the growth of M. aquaticum and L. peploides. The increase of DMF reduced the amounts of total chlorophyll (Tchl) and chlorophyll a(chla) in all aquatic plants, but increased the SOD activity of H. verticillata. Both the SOD activities of M. aquaticum and L. peploides were not affected significantly by DMF, while that of A. philoxeroides showed a rising trend then followed by declining with the increase of DMF, and reached the maximum of 928.7U·gFW-1 at DMF of 400mg·L-1. POD activity of M. aquaticum was not detected in the test. POD activity of A. philoxeroides was the highest among the three aquatic plant species with the maximum value of 16251.25U·gFW-1·min-1 obtained at DMF of 400mg·L-1. The DMF could induce rise of the root activities of H. verticillata, and A. philoxeroides. The root activity of L. peploides increased by 111.7% compared with the control at DMF of 100mg·L-1, and then declined with the increase of DMF. However, the root activity of M. aquaticum showed an opposite trend to L. peploides. When DMF was 400mg·L-1, it decreased from 408.49ugTTF·gFW-1·h-1 to 191.29 ugTTF·gFW-1·h-1.4. The aquatic plants could improve the degradation of DMF, and DMF removal in the aquatic plant-microbe system was 4.3-5.8% higher than that in the microbe treatment. The removal of NH4+ -N and TN were enhanced significantly as well. The NH4+ -N and TN declined to 2.72-5.17mg·L-1 and 5.11-6.56mg·L-1, respectively, which were 69.5-84.0% and 61.5-70.0% lower than the microbe system. The root exudates could not improve the removal of DMF and probably increased the TOC. The TOC removal efficiency of root exudate-microbe system was 62.3-66.2%, lower than the microbe system of 68.6%.5. A strain NLQ capable of using DMF as the sole carbon, nitrogen was isolated from the carbon fibre packing of tank 1. It was identified as Penicillium griseofulvum based on its biochemical/morphological characteristics and homologic analysis of its 18SrDNA sequence. NLQ was not sensitive to DO, and the optimum pH was 6-8. DMF was completely removed in 36h as the initial DMF less than 200mg·L-1. When the initial DMF was as high as 800mg·L-1, removal was slow at the beginning and reached 92.2% in 96h. The concentration of dimethylamine(DMA) and NH4+-N increased with degradation of DMF. The DMA reached the maximum of 30.66mg·L-1 in 24h when the initial DMF was 100mg·L-1, while that of NH4+-N was obtained in 42h with the value of 17.88mg·L-1, accounting for 93.2% of theoretical value. Growth was observed when NLQ was grown on DMA, monmethylamine(MMA), formate, and formamide, respectively, and the order of degradation efficiency was MDA>formate>MMA. The strain showed faint degradation for formamide.6. Mesoporous activated carbon with BET surface area of 1,174.13m2·g-1 was prepared from T. dealbata by phosphoric acid activation. Total pore volume of the derived activated carbon(TDAC) was 0.949cm3·g-1 with an average pore diameter of 3.23nm. FTIR spectrum suggested the presence of abundant carboxyl and hydroxyl groups on the surface of TDAC. The potential of TDAC to remove reactive brilliant blue(X-BR), crystal violet(CV) and methylene blue(MB) was investigated under varying conditions of pH, adsorbent dosage and initial concentration of dye. The results showed that adsorption for X-BR was favored under acid conditions, and adsorption capacity decreased by 60.9% as the pH was increased to 11, while the adsorption for CV and MB were not affected by pH significantly. Adsorption efficiencies for three dyes reached 100% as the adsorbent dosage was 1.0g·L-1 at dyes concentration of 100mg·L-1. All processes for three dyes reached equilibrium within 30 min, which followed the pseudo-second-order kinetic model. The equilibrium data of X-BR fitted well with the Langmuir and the Freundlich models, while those of CV and MB followed more closely the Langmuir model.