Treatment Methods and Process Flow for Livestock and Poultry Wastewater Explained

In the past 10 years, China's suburban "vegetable basket" project has developed rapidly. Intensive, large-scale livestock and poultry chicken farming has risen rapidly. At present, the total annual output of manure from live chickens and other poultry nationwide is as high as 580 million tons, and the total annual discharge of manure water is as high as 6 billion tons. However, the amount of manure water treated by engineering measures in the city accounts for only 25% of the discharge. Due to a lack of funds, the vast majority of these chicken farms do not adequately treat and utilize their manure, and the pollution of the surrounding environment is becoming increasingly serious. Many chicken farms stink to high heaven, with swarms of mosquitoes and flies, nitrate levels in groundwater seriously exceeding standards, and infectious diseases and parasitic diseases prevalent in a few areas. Large-scale wastewater has reached the point where it must be treated.

On layer hen farms, chicken manure is mixed with spilled residual feed, water dripping from feeding and drinking, and flushing water from manure channels to form a chicken manure mixed liquid. Chicken houses are frequently flushed, and hatcheries are also regularly washed and disinfected, producing large amounts of wastewater. Chicken manure wastewater not only contains high concentrations of organic pollutants and high concentrations of solid suspended matter, but is also rich in nutrient elements such as nitrogen and phosphorus, with a high ammonia nitrogen content, which brings great difficulties to the biochemical treatment of chicken manure wastewater, especially denitrification treatment.

If pollutants such as manure from livestock and poultry farms are not treated and are discharged or disposed of improperly, they pollute the ground, soil and groundwater. The pollution of water bodies and soil by manure wastewater mainly comes from the harm caused by organic pollutants and nutrients such as nitrogen and phosphorus.

1. Organic pollutants

Manure contains large amounts of carbon-containing compounds, ammonia-containing compounds and other putrefactive organic matter. After entering a water body, it first seriously makes the water turbid, turns the water yellow, and makes the smell foul. Under the action of microorganisms, when large amounts of dissolved oxygen in the water are consumed, the dissolved oxygen is exhausted, organic matter undergoes anaerobic decomposition, producing a variety of malodorous substances; the water body turns black and stinks, water quality deteriorates, and it is unfit for drinking.

2. Nitrogen and phosphorus nutrient pollution

Nitrogen and phosphorus are the main nutrient pollutants in chicken farm excrement. During the process of organic decomposition, organic nitrogen and phosphorus are also mineralized into inorganic nitrogen and phosphorus. Most nitrogen-containing compounds are oxidized into nitrate, part of which remains in the topsoil, while another part seeps into the ground, and over time will pollute groundwater sources. Wastewater containing excessive phosphorus flows into ditches and ponds, causing eutrophication of the water body, which can cause algae and other plankton to multiply and grow wildly, leading to a decrease in dissolved oxygen content in the water and the production of various toxins, directly affecting fish growth. Due to the massive reproduction of algae, the turbidity of the water is increased, impairing the photosynthesis of aquatic plants and algae and causing them to die; the dead algae and aquatic plants rot and decompose under anaerobic conditions, leading to deterioration of the water body and thus harming the ecological environment.

3. Mineral element pollution

In the livestock and poultry breeding industry, salt is often added to feed to enhance the appetite of livestock and poultry, which leads to an increase in the salt content of manure and urine, directly affecting animal health and the food safety of livestock products, polluting the soil, and being unfavorable to crop growth. The implementation of this project will help improve the pollution of soil and water bodies by livestock and poultry manure.

Chicken manure contains a relatively high amount of sand, especially breeder chicken manure; the amount of grit and shells added to the feed is 8%, which is carried into the manure through the digestive tract. In addition, chicken manure contains a relatively large amount of chicken feathers, especially during the molting period.

Since the "Ninth Five-Year Plan", China has carried out a great deal of research and exploration on the treatment processes and technologies for manure wastewater, conducted experiments and practices in all aspects of manure wastewater treatment, and achieved proven and effective successful experience, gradually forming a treatment process based mainly on biochemical treatment and combining biochemical with physicochemical treatment. Commonly used biochemical methods include the activated sludge process, the biofilm process, the anaerobic-aerobic combined process, and the hydrolysis-acidification and aerobic combined process, among various other processes. Engineering practice has confirmed that aerobic treatment after solid-liquid separation of manure wastewater from medium and large chicken farms is feasible and highly efficient, while for smaller-scale operations the hydrolysis-acidification and aerobic combined method is more suitable. Adopting anaerobic digestion can, on the one hand, reduce energy consumption and lower operating costs, and on the other hand can also recover methane gas and make use of it, thereby achieving the effect of waste utilization.