Methods for treating aquaculture wastewater

Methods for treating aquaculture wastewater
Anticipated by the significant biochemical attributes of aquaculture wastewater, biochemical treatment technology has progressively emerged in treating such waste. Biochemical treatment is classified into anaerobic biochemical treatment, aerobic biochemical treatment, and natural methods, determined by their diverse working principles.
① Anaerobic Biochemical Treatment
For wastewater rich in organic substances from cultivation farms, anaerobic digestion technology efficiently removes substantial quantities of soluble organic matter at modest operating costs, demonstrating COD removal rates that exceed 85% to 90%, concurrently eliminating infectious bacteria, which prove beneficial for disease prevention in cultivation farms.
However, utilizing aerobic technology directly to process aquaculture wastewater post solid-liquid separation, while potentially saving a one-time investment by 20%, results in high power consumption, with electricity and water consumption reaching up to 10 times that of anaerobic treatment. Consequently, the long-term operating costs impose a substantial economic burden on the aquaculture farm.
Presently, numerous anaerobic processes are employed to treat manure in aquaculture farms, with the most frequently utilized ones including anaerobic filters (AF), upflow anaerobic sludge beds (UASB), composite anaerobic reactors (UASB+AF), two-stage anaerobic digestion, and upflow sludge bed reactors (USR). In recent years, anaerobic digestion, also referred to as biogas fermentation technology, has been extensively implemented in waste treatment in livestock farms. By the close of 2002, the number of large and medium-sized biogas projects in livestock and poultry farms in China had surpassed 2000, positioning it as one of the nations with the highest number of biogas facilities globally.
② Aerobic biochemical treatment
Aerobic treatment pertains to a process of employing aerobic microorganisms to treat aquaculture wastewater. Aerobic biological treatment methods delineate into two categories: natural aerobic treatment and artificial aerobic treatment.
The natural aerobic biological treatment method is an approach of purifying wastewater utilizing microorganisms in natural water and soil, also recognized as natural biological treatment method. Mainly, this comprises two types of methods: water purification and soil purification. The former primarily encompasses oxidation ponds (aerobic ponds, facultative ponds, anaerobic ponds) and aquaculture ponds. The latter primarily encompasses land treatment (slow infiltration, rapid filtration, surface runoff) and artificial wetlands. This natural biological treatment method not only possesses low infrastructure costs and low power consumption, but also exhibits higher removal rates for recalcitrant organic matter, nitrogen and phosphorus nutrients, and bacteria than conventional secondary treatment, with some achieving the effect of tertiary treatment.
Additionally, under specific conditions, this method, when integrated with sewage irrigation, can achieve the resource utilization of sewage. The primary drawbacks of this method are its extensive footprint and susceptibility to seasonal fluctuations in treatment effectiveness. However, if the farm is petite and there are abandoned ditches, ponds, and mudflats nearby for utilization, this method should be chosen whenever possible to economize investment and treatment costs. Artificial aerobic biological treatment is a wastewater treatment methodology that employs artificially augmented oxygen supply to enhance the activity of aerobic microorganisms.
This method principally includes activated sludge process, biological filter, biological turntable, biological contact oxidation process, sequencing batch reactor (SBR), anaerobic/aerobic (A/O) and oxidation ditch process. In terms of treatment effectiveness, the contact oxidation method and biological rotary disc method exhibit superior treatment effects compared to the activated sludge method. Although the treatment effect of the biological filter is also commendable, it is prone to filter clogging.
Oxidation ditch, SBR, and A/O processes are all advanced activated sludge processes. The effluent from the oxidation ditch possesses excellent water quality and generates minimal sludge. It can also be used for denitrification treatment of sewage, but it has a low BOD load, an expansive footprint, and hefty operating costs. The SBR method has a high degree of automation control and can thoroughly treat sewage, but its disadvantage is that the BOD load is small and the one-time investment is also substantial.