| With the development of economy and the improvement of standard living, large amount of wastewaters are generated. The wastewaters from industry, agriculture and housing settlements contain sulfur compounds. Sulfur pollution has already posed hazardous effects on human health and ecological safety. Hence, how to treat such wastewater economically and efficiently is one of the most popular environmental topics in recent years. It has been shown that some bacterial species like Thiobacillus denitrificans can oxidize sulfide to elemental sulfur simultaneously reducing nitrate to dinitrogen. For such reasons, the simultaneous anaerobic sulfide and nitrate removal process has been developed. In this research, the process was studied from operating conditions and microbial properties. Major research results are as follows:1) The simultaneous anaerobic sulfide and nitrate removal process in inorganic condition was studied. It was discovered that the start-up course of the process was fast by using Upflow Anaerobic Sludge Blanket (UASB) reactor. The volumetric removal rates of sulfide and nitrate were 0.323 kg·m-3·d-1 and 0.071 kg·m-3·d-1 after 26 days'operation, which had reached the reported level in liteature. The results also showed that the process could hold a high sulfide and nitrate removal loading rate of 3.73 kg·m-3·d-1 and 0.80 kg·m-3·d-1, respectively, under steady state. It was capable of tolerating high influent substrate concentration (580 mg-L-1 and 110 mg-L-1). It was capable of tolerating short hydraulic retention time (HRT). When HRT was 0.13 d, the removal percentage of sulfide and nitrate were higher than 99% and 92%, respectively.2) The operating conditions of simultaneous anaerobic sulfide and nitrate removal process were investigated.①The effect of influent substrates on the performance of simultaneous anaerobic sulfur and nitrogen removal process was investigated. It was discovered that the process using nitrate as electron accepter was better than that using nitrite as electron accepter. The maximum acceptable sulfide concentration and volumetric removal rate of simultaneous anaerobic sulfide and nitrate removal process were higher than those of simultaneous anaerobic sulfide and nitrite removal process. The sludge had better tolerance to electron donor than electron accepter. Judged by sensitivity ratio, the activated sludge was more tolerant to sulfide, while no significant differences were found in respect of using nitrate or nitrite as influent substrate. The activated sludge was less tolerant to nitrate, the least tolerant to nitrite. The sludge had slightly better affinity on nitrite than nitrate, whose half saturation values were 0.26±0.08 mg·L-1 and 0.35±0.09 mg·L-1, respectively. The minimum reaction time (5h) for nitrate and sulfide was relatively longer than that for nitrite and sulfide as influent substrates (4 h).②The effect of sulfide to nitrate (S/N) molar ratio on the performance of simultaneous anaerobic sulfide and nitrate removal process was investigated. It was discovered that the process performance at molar S/N ratio of 5:2 was significantly better than those at S/N molar ratios of 5:5 and 5:8, based on capacity, stability and selectivity. The volumetric sulfide and nitrate removal rates at molar S/N ratio of 5:2 were 4.86 kg·m-3·d-1 and 0.99 kg·m-3·d-1, respectively, which were higher than those at the other S/N molar ratios. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios, which showed better stability. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. Moreover, the ratio of converted sulfide to converted nitrate tended to approach 5:2 during the operation.③The effect of pH and alkalinity on the performance of simultaneous anaerobic sulfide and nitrate removal process was investigated. It was discovered that the process performance was better when the reaction pH was controlled between 6.9 and 7.1 than that when the influent pH was controlled between 7.5 and 8.0. In order to keep a neutral condition, the alkalinity should be adjusted at 454.1±40.5 mg CaCO3·L-1. The alkalinity change in the process can indicate the style and extent of the dominant reaction. When S/N ratios were 5:2,5:8 and 5:5, the ratios of removed sulfide to decreased alkalinity were 2.98,2.56 and 6.41, respectively.④The effect of substrate shock on the performance of simultaneous anaerobic sulfide and nitrate removal process was investigated. It was discovered that based on the response to the shock loads, the reactor performance could be divided into three stages:disturbance, inertia and recovery periods. The effluent sulfide concentration was a sensitive parameter, which increased up to 18 times of that at steady state and could be used as an indicator of the reactor performance. The effect of the shock loads on the reactor performance was related to the intensity of the shock loads. The responsive strength increased with the increasing intensity of shock loads. The performance was able to recover from disturbances at all the tested shock loads. In 30 hours (7.5h), all the performance indices of the reactor could return to the initial stable state.3) The microbial properties of simultaneous anaerobic sulfide and nitrate removal process were studied.①The physical and ecological characteristics of cultivated sludge for simultaneous anaerobic sulfide and nitrate removal were studied. It was discovered that the cultivated sludge showed good settlability, whose diameters, settling velocities and density were 0.54-3.99 mm,56.13-171.43 m·h-1 and 1.08 kg·m-3, respectively. It was irregular-shaped and was composed of subunits (such as zoogloea and floc) under optical microscope. It was observed that the dominant microorganisms on the surface were bacilli, but those in the inner were diversiform under scanning electron microscope, The results from PCR-DGGE analysis exhibited rich diversity of microbial populations and dominant kinds of microorganisms Proteobacteria.②The bacteria responsible for simultaneous sulfide and nitrate removal were isolated and identified. It was discovered that the bacterial strains CB and CS were isolated from the UASB reactor working under steady-state with sulfide and nitrate as electron donor and acceptor, respectively. Based on electron microscopy, physiological test and 16S rDNA phylogenetic sequence analysis, the isolate CB was very close to Bacillus pseudofirmus and the isolate CS was very close to Bacillus hemicellulosilytus and Bacillus halodurans. Both the isolate CB and the isolate CS are able to use nitrate for sulfide oxidation. The isolate CS has greater capability to oxidize sulfide with nitrate as electron acceptor. According to Biolog carbon source utilization test, the isolate CB can only use a few of carbon sources, while the isolate CB can use a lot of carbon sources. Some carbon sources, such as glucose, galactose, arabinose, can be used to promote the growth of these autotrophic bacteria.
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