Studies on promoting effect of nutrient addition on aquacultural wastewater purification of commercial microorganism products

The promoting effect of nutrient addition on aquacultural wastewater purification of microorganism products, SYMCORE BZT^TM was investigated， and furthermore, the relationship between removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N) and nitrite nitrogen (NO₂^--N) and the ratio of C∶N∶P was studied. The experiments were composed of two parts. Part I consisted of one control group and two trial groups, promoting effect of nutrient addition on removal rate of microorganism was proved. Part II was made up of one control group and 15 trial groups to analyze the relationship between the mount of added nutrients and the removal rates of pollutants. Moreover, the relationship between the ratio of carbon, nitrogen and phosphorus and the removal rates of COD, NH₄⁺-N and NO₂^--N was calculated, and the mathematics models were set up. The results showed that the purification ability of microorganism products was significantly improved by adding suitable nutrients. The removal rates of COD, NH₄⁺-N and NO₂^--N of the treatment group increased 21.92%,34.43%,57.41% by adding glucose and 30.02%, 53.45%, 15.08% by adding phosphate compared with the control, respectively. At the same time, the amount of phosphate was found insufficient in control group. The removal rates for COD, NH₄⁺-N and NO₂^--N were the highest, 97.07%, 96.88% and 93.41%, when the ratio of C∶N∶P was 62.5∶4.85∶1，37.5∶4.51∶1 and 25∶2.97∶1, respectively. The relationship of glucose and phosphate concentration with COD, NH₄⁺-N and NO₂^--N removal rates could be described by quadratic equations, V=aX²+bX+c. The individual COD, NH₄⁺-N and NO₂^--N removal rates of the microorganism products are positively correlated with the concentration of glucose and phosphate in range of 0-40 mg/L and 0-1 600 mg/L, respectively. The process of microbial remediation could be featured as three sequential stages：Firstly, dissolved organic matter (DOM) was degraded; secondly ammonia was oxidized; and at last, nitrite was oxidized. From day 1 to day 7, DOM was directly utilized as the carbon and nitrogen sources of the heterotrophic bacteria．The removal rates of COD at this stage were significantly higher than those of the control. From day 7 to day 13, bacteria mainly utilized ammonium as nitrogen sources and produced nitrite. So the concentration of NH₄⁺-N reduced sharply, while NO₂^--N concentration increased suddenly. From day 13 to 19, NO₂^--N concentration decreased rapidly, because the nitrite was oxidized to nitrate. This paper supplied theoretical and technical foundation for the biopurification of aquaculture wastewater and the extending application of microbial products.