Autotrophic denitrification for treatment of wastewater with high concentration of sulphur and nitrogen compounds

Laburpena

Autotrophic Denitrification supposed a good alternative for treatment of those effluents with low or none organic matter content. In the Autotrophic Denitrification bacteria of the type Thiobacillus combine nitrate and reduce sulphur compounds to yield nitrogen gas and sulphate or elemental sulphur. The process is autotrophic, so it not necessary the addition of organic matter. Since reduced sulphur compound are required as electron donor to reduce of nitrate. The present thesis is concentrated on study of Autotrophic Denitrification process. The main objective of this project was the operation of a Sequencing Batch Reactor (SBR) under autotrophic denitrifying condition for simultaneous removal of nitrate and sulphide. In this thesis enrichment of autotrophic denitrifying biomass was development from anaerobic sludge, for further application of the process. Batch reactor was selected as system to enrichment of autotrophic denitrifying biomass. After the several feeding, autotrophic denitrifying biomass was enriched. At end of enrichment the biomass obtained was able to carry out autotrophic denitrification with different sulphur compound as electron donor (S2O32-, S2- and stored sulphur). Obtained that maximum Autotrophic Denitrifying Activity with thiosulphate 211 mg NO3--N (g SSV)-1 d-1. The SBR is a suitable technology to carry out the autotrophic denitrification of wastewaters containing sulphide and nitrate. Which was able to treat loading rates of 0.45 g NO3--N L-1d-1 and 0.45 g S2- L-1 d-1 were treated with removal efficiencies around 67% and 100%, respectively. Control of pH is an important parameter to ensure optimum condition for microbial activity. Combination of nitrification/autotrophic denitrification could be a possibility for the post-treatment of fish cannery effluent. The operational costs are lower than those of the conventional nitrification/denitrification processes. Under stoichiometric conditions the maximum nitrate concentration able to treat not exceeds the Ki (279 ± 4.38 mg NO3--N L-1) and the maximum nitrite concentration not exceeds the IC50 value (36 mg NO2--N L-1). The study of the phylogenetic composition of the biomass gave as results that the predominant population was Thiobacillus denitrificans with a 99% similarity, anothers two groups able to use a sulphur source were also detected, one close to phylum Chlorobi and another close to candidate division JS1 with 95% and 94% similarity.