Discussion on technologies and experiences in treating aquaculture wastewater

Anaerobic biogas is the current mainstream approach, with the key issues being the utilization of biogas and its desulfurization. Small biogas generators and desulfurization agents have now all been developed. Also, to make it economically viable, it would be better to consider things from the perspective of regional recycling.

The main challenge in treating aquaculture wastewater lies in the conflict between treatment costs and the required standards. Currently, the anaerobic + aerobic process can remove most pollutants, but there is still a gap to meet first-class discharge standards. This is reflected in the fact that treatment costs are proportional to the discharge standards: the higher the standards, the higher the costs. This creates a conflict with the profitability of farmers, as if pollution is controlled but there is no profit, then why would anyone engage in aquaculture? Therefore, **subsidies in this area should be increased. Furthermore, since aquaculture wastewater is closely related to the scale of aquaculture, a larger scale results in a lower amount of pollution per unit, and thus the treatment costs are relatively lower as well. In terms of treatment methods, anaerobic digestion to produce biogas is the mainstream approach. However, there are also issues with the utilization of biogas: firstly, the investment required for desulfurization equipment is high; secondly, biogas is mainly used for heating boilers and cannot be used for power generation. As a result, we are lagging behind in terms of technological investment in this area. It is necessary to provide more support for the promotion and use of biogas, so as to reduce the costs incurred by farmers, and then the treatment of livestock wastewater may no longer be a problem.

I have a few personal suggestions regarding ways to improve the difficulty of treating aquaculture wastewater; please feel free to correct me: 1. The anaerobic stage is indeed a challenging part, but the mature technologies available today can already address this issue. It maintains a high removal rate (over 80%) even when operating at low temperatures. 2 Another challenge with aquaculture wastewater is the utilization of biogas. Since large-scale farms generate relatively little biogas from their wastewater, it is not economical to invest in separate biogas boilers; it is recommended to use a mixture of natural gas or other fuels, with gas boilers being designed accordingly based on specific circumstances. 3 The main compliance issues are excessive COD and ammonia nitrogen levels; it is recommended to reduce aerobic processes and compensate for this using artificial wetlands. 4 Overall optimization to achieve a circular economy that integrates wastewater treatment, energy utilization, and aquaculture with agriculture.

The wastewater from livestock farming and dairy processing is treated together, using EGSB+SBR or three-stage contact oxidation. At present, the manure and wastewater generated by livestock farming constitute a pollution burden on water bodies that is already, or is becoming, a greater source of contamination than industrial wastewater and domestic sewage. Wastewater from livestock and poultry farms mainly includes urine, some manure, and water used for cleaning the breeding facilities. This type of wastewater has a high concentration of organic matter, numerous suspended solids, high levels of ammonia nitrogen, and a strong odor. The wastewater treatment plant for livestock and poultry farming at ×× Agricultural University, which has now been built, not only addresses the serious problem of pollution caused by wastewater from livestock and poultry farming but also contributes to the development of effective treatment methods for such wastewater. In particular, the combined ABR2CASS treatment process proves effective; monitoring results show that after treatment with this process, parameters such as CODCr, ammonia nitrogen, and SS meet the standards set for first-class discharge of wastewater. (1) The wastewater treatment process based on air flotation 2ABR2CASS2 wetlands and ecological ponds has the following advantages: it improves the efficiency of wastewater treatment, prevents the generation of odors, has a strong capacity to handle shock loads, and results in less excess sludge. (2) Apart from the need for a lift pump to provide power for transporting the wastewater from the regulating tank to the air flotation tower, the wastewater can flow by gravity to the next processing stage, thereby reducing operating costs. The current operating cost is 1,117 yuan per Pm3. (3) The operation and management of this wastewater treatment plant are very convenient. (4) For the treatment of wastewater from livestock and poultry farming, it is necessary to strengthen the recovery and comprehensive utilization of materials. Dry manure should be collected before washing, and then used together with the sludge generated during wastewater treatment to produce organic fertilizer; the biogas produced by ABR tanks is utilized as an energy source, thereby reducing the operating costs of the facility. (5) Before wastewater enters the grid tank, dry manure removal procedures and rainwater-sewage separation technologies should be implemented to reduce the load on the sewage treatment plant; the sludge in the regulating tank must be cleaned regularly to prevent blockages in the lift pumps. Based on actual operational experience, the anaerobic UASB + aerobic biological treatment process can be applied in the treatment of dairy wastewater, enabling the reduction of operating costs associated with wastewater treatment as well as minimizing the amount of sludge generated during this process. However, using this process also presents issues such as complex operation and management, unstable treatment results, and safety hazards. The anaerobic system must be designed in strict accordance with fire safety regulations, and during operation and management, precautions must be taken regarding fire prevention, explosion prevention, and protection against poisoning, all in strict compliance with operating procedures. If a safety accident occurs during operation, the consequences will be unimaginable. The problems with treatment efficiency that occur during the operation of anaerobic UASB are mainly due to the influence of scum in dairy wastewater and an inappropriate selection of the three-phase separator. To ensure the stable operation of the anaerobic system, it is necessary to address the issue of scum in the UASB reactor, and select a three-phase separator that can operate stably even when there is a large amount of scum. For wastewater such as cold drinks and yogurt that generate large amounts of scum, greater attention should be paid to the pretreatment of the scum and the selection of the type of three-phase separator. Furthermore, since anaerobic treatment of dairy wastewater makes it difficult to form granular sludge, a high organic load cannot be used in the design of anaerobic systems; the typical design load should be between 2 and 3 kg/m3·d, otherwise it will affect the treatment efficiency and stable operation of the entire system.

Pre-treatment using physical methods is a popular approach nowadays; I think that the SS levels after such treatment will still be high, and the requirements for anaerobic design become even more stringent. Therefore, it is still better to opt for IC instead of UASB. There are several advantages: 1 a higher removal rate at higher SS levels; 2 prevention of sludge leakage; 3 lower investment costs