The Set-up And Operation Of Denitrifying Sulfide Removal Process

Denitrifying sulfide removal (DSR) process is a new established wastewater treatment technology based on denitrifying process and sulfide oxidization process. DSR is cost effective and operation easily to treat the wastewater with nitrate and sulfide simultaneously. A lot of research work have already done on the design and operation of DSR process. However, there are still many topics should be examined before the process could put in industrial operation. The work is focus on several subjects of the set-up and operation of DSR process.Rapid formation of denitrifying sulfide removal granules is of practical interest to start up an expanded granular sludge bed reactor for wastewater treatment. This study demonstrates that methanogenic granules can be easily acclimated into DSR granules in one day, removing all 1.30 kg m-3 d-1 sulfide and >90% of 0.56 kg-N m-3d-1 nitrate into di-nitrogen gas. Under high loadings, reactor performance, however, declined. Under high loading rates, sulfide first inhibited the heterotrophic denitrifier (Caldithrix sp.), thereby accumulating nitrite in the system; the autotrophic denitrifier (Pseudomonas sp. C23) was then inhibited by accumulated nitrite, leading to breakdown of the entire DSR process.Denitrifying sulfide removal (DSR) processes simultaneously convert sulfide, nitrate, and chemical oxygen demand from industrial wastewater into elemental sulfur, dinitrogen gas, and carbon dioxide, respectively. The failure of a DSR process is signaled by high concentrations of sulfide in reactor effluent. Conventionally, DSR reactor failure is blamed for overcompetition for heterotroph to autotroph communities. This study indicates that the elementary sulfur produced by oxidizing sulfide that is a recoverable resource from sulfide-laden wastewaters can be reduced back to sulfide by sulfur-reducing Methanobacterium sp. The Methanobacterium sp. was stimulated with excess organic carbon (acetate) when nitrite was completely consumed by heterotrophic denitrifiers. Adjusting hydraulic retention time of a DSR reactor when nitrite is completely consumed provides an additional control variable for maximizing DSR performance.Copper biosorption processes by two kinds of pretreated powdered anaerobic granular sludge: methanogenic anaerobic granules and denitrifying sulfide removal (DSR) anaerobic granules were investigated with batch experiments. Some important influence factors affecting the biosorption process such as pH, temperature, and initial copper concentrations were examined. Also, the characteristics of the anaerobic sludge were analyzed by FT-IR spectra, SEM image, surface area and elemental analysis. Both pseudo first–order and second–order kinetic models were applied on describing the biosorption process, and the second–order kinetic model could fit the biosorption process better. The Freundlich and Langmuir models were used for describing the adsorption equilibrium data, and only Freundlich model could fit the equilibrium data well. The experiments results showed that the methanogenic sludge was more effective in copper biosorption than DSR sludge, the maximum biosorption capacity of the former was 39.6% higher that the later. The mechanisms of the different efficiency of biosorption according to the different kinds of sludge were discussed, and the conclusion suggested that the growth environment and biochemical reactions during the growth of biomass could largely affect the structure of the sludge, thus the methanogenic sludge had higher surface area, and then its biosorption capacity was increased. However, compared to other kinds of biosorption materials, both DSR sludge and methanogenic sludge have an ideal biosorption capacity on copper adsorption.