Cultivation And Characters Of The Aerobic Granules For Ammonium And Sulfide Removal In SBR System

The processing and utilization of agricultural products such as maize, soybean, wheat and potato can generate a large amount of organic wastewater which contains high concentrations of sulfate and ammonia. Researchers conducted an extensive investigation of the technologies and equipments of anaerobic biological treatment of sulfate-rich wastewater, However, in the process of anaerobic treatment, sulfate changed into a kind of toxic sulfide that was highly corrosive to the equipments, besides, the ammonia could not remove effectively,it required a further treatment to resolve the problem of wastewater pollution from agricultural products processing. There are several defects in the currently-adopted aerobic sulfide and ammonium removal technology, namely, complex processing, big investment and high operating cost. Therefore, to seek an advanced, low-cost and highly-efficient wastewater treatment is of great significance to the development of agricultural products processing business.Compared to the conventional activated sludge flocs, the newly-developed aerobic granular sludge technology have Several advantages,such as high volumetric loading, good settling ability, small occupying space, low investment and so on. Owing to the restrict mass transfer of the dissolved oxygen in granules, so inside the aerobic granules it form Aerobic zone, Anoxic zone and anaerobic zone, which enables the co-existence of aerobic and anaerobic microorganism and realizes simultaneous removal of many kinds of pollutant. The aerobic granular sludge technology has a good prospect.Drawing on the properties of aerobic granular sludge, this research investigated the cultivation and characters of the aerobic granules for ammonium and sulfide removal, especially the removal process and influencing factors, which will provide theoretical basis for the application of aerobic granules in agricultural products processing wastewater treatment.The main results are as follows:(1) Cultivation and characters of the aerobic granules for ammonium and sulfide removal in a sequencing batch reactor were studied. Using anaerobic granular sludge as seed sludge, the aerobic granules for ammonium and sulfide removal were cultivated fed with synthetic ammonia and sulfide-rich wastewater under controlled operational conditions in 21 days. The diameter of most of the aerobic granules was about 1-1.5 mm and the SVI was 30-40 mL/g. The granule was dominated by Brevibacterium, and wrapped by a large number of filamentous bacteria. When the sulfide influent, COD and NH₄⁺-N concentration were 50mg/L,550mg/L and 55mg/L, the removal efficiencies of S^2-, COD and NH₄⁺-N were >99%, >80% and >99%, respectively.(2) The influence of sulfide on removal effect and sludge stability was investigated. When the COD and NH₄⁺-N concentration were 550mg/L and 55mg/L and the S^2- concentration increased from 50mg/L to 300mg/L, the removal efficiency of S^2- maintained above 99%, and the removal efficiencies of COD and NH₄⁺-N were slightly decreased at the early stage of concentration increase, but after one week, they could reach above 80% and 99% respectively. However, when the S^2- concentration exceeded 100mg/L, filamentous bacteria would overgrowth and SVI >100mL/g, so the system would become instable.(3) The microbial population of aerobic granules for ammonium and sulfide removal was also studied. The PCR-DGGE analysis showed that: during stable operation, the microbial population of aerobic granules was comparatively rich and their structures were steady. The population mainly includedβ-proteobacterium and Uncultured Bacteroidetes bacterium, which accounted for 27.27% and 18.18%, respectively. Dominant consortium in granules were denitrifying bacteria (Thauera sp.), Heterotrophic Nitrification Bacteria (pseudomonas alcaligenes)and Uncultured Thiothrix sp..(4) The removal process and influencing factors were studied. The nitrogen removal pathways including nitrification and denitrification, Simultaneous nitrification and denitrification and heterotrophic nitrification and denitrification in the SBR system. Sulfide was removed mainly through the biological oxidation processes of Uncultured Thiothrix sp.. DO had a great impact on the removal efficiency of ammonium and sulfide.(5) The reason why aerobic granules could keep a highly-efficient ammonium removal performance under high concentration of sulfide was also discussed. The sulfide removal mainly took place in the first 30 minutes of the cycle of the SBR, while ammonium removal in the range of 30-120min.The SBR reactor showed high removal capacity of NH₄⁺-N under the high S^2- concentration, which was possible due to the layered structure of aerobic granules or the characteristics that sulfide could be fast oxidized prior to the ammonium.(6) The mass transfer and kinetics of aerobic granules were also considered. The mass transfer of DO and sulfide showed more influence on nitrification and denitrifying, while the mass transfer of ammonium showed little. The kinetic models of aerobic granules for COD and NH4+-N removal were as follows:...