Design And Optimization Of Wastewater Treatment In Intensive Fish Culture

With the development of aquaculture, the culture environment and the water quality have been degraded greatly because of the wastewater drainage. The main contamination in the wastewater is the remanent bait, feces, and kinds of nutriment, all of which contribute much to the increase of BOD5 and COD in the water.The accumulation of ammonia, nitrite and nitrate, which are the main productions as the nutriment decomposes, does harm to the living fish and incurs the water enrichment. Therefore, to decrease the ammonia/nitrite/nitrate concentration or to remove them completely is a feasible approach to remain high level water quality and avoid environment pollution. In the traditional intensive fish culture, the water quality problem could be solved by flow water, aeration, temperature control, and sterilization. At present, many wastewater treatment means have been devised, such as to cultivate a harmonious environment which is suitable for both fish and alga, to immobilize bacteria for ammonia removal, to use ozone for BOD5 removal and to use ultraviolet radiation for sterilization.This paper studied the special growth rate of Ulva pertusa and ammonia absorbing rate as the temperature and salinity varied. The results showed that the temperature and salinity influenced Ulva pertusa's SGR much. The suitable temperature range for Ulva pertusa is 15~25C and salinity is between 15~40. Its maximum daily SGR is 12.3%. The bigger the salinity, the less Ulvapertusa absorbs ammonia.The result of Ulvapertusa wastewater treatment experiment showed that the preferential absorbing sequence is NH4-N, NO3-N, NO2-N; to use Ulva pertusa for ammonia removal could get a low concentration of ammonia; the phosphate concentration and COD changed less during the experiment; illumination influences the ammonia absorbing rate to some degree, but has no influence to nitrite.Four wastewater treatment means were devised and the removal results were compared. The experiment showed: the treatment means of activated sludge with Vlva pertusa could decrease BODs concentration and remove ammonia and nitrate effectively, but this means needed a period of time to adapt and adjust; the means of activated sludge with immobilized bacteria removed much nitrate, most of which came from the contribution of immobilized bacteria, and all the removal rate of BOD5, ammonia and nitrate decreased in this treatment means because of the solution of immobilized bacteria.Consulting the above experiment results, an integrated wastewater treatment means was devised. An activated sludge tank and alga tank were designed to remove organic compounds and TAN respectively. Water temperature could be controlled by some kind of instrument and the UV radiation was designed to sterilize the circulation water. Supposing the area of fishpond is 1000m2 and 0.8m deep, the volume of aeration tank and sedimentation tank, time of aeration, quantity of atmosphere needed, quantity of increased sludge were caculated.