| Biological purification is the core of water treatment technology in recirculating aquaculture system (RAS). The principle is that the biofilm can adsorb, absord, decompose and transform suspended particulate matter, soluble organics and ammonia, nitrite and other soluble inorganic salt in the water. The constituent elements of the biofilm are all kinds of nitrification and denitrifying bacteria, which are very sensitive to the change of environment conditions. It is important yet difficult to control the cultural environment in the production process of RAS, and this usually affects the efficiency and smooth running of the system.This study focuses on the aquaculture waste removal kinetic characteristics of the biofilter, and its efficiency of waste water treatment as affected by the environmental conditions. Findings in this study may help optimizing the working conditions of biofilter, so as to provide theoretical basis for optimizing RAS design and operation. The main contents and conclusions are as follows:1. The study was carried out in an experiment recirculation system, with biochemical cotton (polypropylene) as the biological carrier and inoculated by an aquaculture probiotics. Waste water from a marine finfish aquaculture tank was used in this system to test the purification efficiency of the biofilter. Before the experiment, ammonium chloride and glucose were added to the mariculture wastewater. Observation of the change in color by naked eye and examination of the microstructure by scanning electron microscopy (SEM) of the biofilm were done to determine the start-up and maturation of the biofilm. Colonizing process of the microorganisms in the biological carrier were explored. As the biofilm reached maturition, the types of bacteria and bacterial content were identified by plate count method, while the composition of the biofilm was determined microscopically. It was found that, biofilm colonization mature lasted 45 days, the surface of the biofilter was covered by zoogloea, with a certain amount of diatoms, chlorella and a small amount of protozoans. The contents of heterotrophic bacteria, nitrite bacteria, nitrification bacteria and denitrification bacteria in the zoogloea were 3.79×107cfu/mL, 4.40×106cfu/mL,3.09×106cfu/mL and 1.58×105cfu/mL respectively. During the maturation process, the microbial community in the zoogloea was gradually formed, and eventually reached a relatively stable state.2. Water purification experiment was done on on the experiment recirculation system using mariculture wastewater, which was enriched by ammonium chloride and glucose. Water quality index removal rate of the biofilter was studied at different water temperature, dissolved oxygen (DO), salinity, and pH. It was found that, water temperature of 28℃, DO 6.00mg/L, salinity 25 and pH 7.5 were the optimum conditions for water purification of this experimental RAS. Under these conditions, the water treatment efficiency was higher, the water quality index removal rate was greater, and the outlet water quality was better. When the water temperature was 28℃, the removal rate of CODMn, NH4+-N, NO2--N and PO43--P were 69.3%,93.7%,93.7% and 19.4%, respectively. When the DO was 6.00mg/L, the removal rate of CODMn, NH4+-N, NO2--N and PO43--P were 72.8%,91.7%,97% and 15.6%, respectively. When the salinity was 25, the removal rate of CODMn, NH4+-N, NO2--N, NO3--N and PO43--P were 57.1%,98.4%,99.9%,100% and 42%, respectively. When the pH was 7.5, the removal rate of CODMn and NH4+-N were 72.8% and 93.3%, respectively. Water temperature, DO, salinity and pH were important factors for the growth and metabolic activity of the microbes in the biofilter, and these are, sometimes decisive on the success of the RAS. |
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