Research On Treating Dairy Wastewater With Freezing-thawing And Disturbed Soil

Dairy wastewater is a kind of organic wastewater with high concentrations. It has several characteristics, such as high organic content, good biodegradability and so on. Dairy wastewater could cause serious pollution to the environment, so it must be treated before dischaging. At present, the main methods of treating dairy wastewater are physicochemical and biochemical technology at home and abroad. But these methods have many disadvantages, such as long process, high cost of construction and operation, instability treatment effect and so on. Therefore it’s necessary to find a better way to treat dairy wastewater.In this paper, sewage land treatment and freezing-thawing alternation were combined to treat dairy wastewater. The main researchs were as follows:(1) After freezing-thawing alternation, the differences in soil physical and chemical properties between treatment and control experiment.(2) The water-soil ratio when soil particles began to move.(3) The removal efficiency of TN(total nitrogen) from dairy wastewater with disturbed and undisturbed soils. The results showed that:(1) During the freezing and thawing, soil porosities of treatment and controlled trials were 50.80% and 47.04%, and that were 43.33% and 41.07% after freezing-thawing alternation. The latters were 7.47% and 5.97% lower than the formers, respectively. It indicated that freezing and thawing action can increase soil porosity, thus improving the treating capacity of soil.(2) During the freezing and thawing, the clay, sand and gravel contents in the soil of treatment were 10.20%, 34.04% and 55.76%, and that of control were 7.07%, 29.42% and 63.51%. The clay and sand contents in the soil of treatment were higher than those of control. The soil nitrogen content of treatment and control were 0.707 and 0.649 g·kg-1. Among them, the clay nitrogen content were 1.035 and 1.097 g·kg-1, and the sand nitrogen content were 0.798 and 0.839g·kg-1, and the gravel nitrogen content were 0.593 and 0.510 g·kg-1, respectively.(3) The water-soil weight ratio was about 4.60 to 1 when soil particles began to move.(4) The research on nitrogen removal efficiencies of dairy wastewater with disturbed and undisturbed soil in September and October showed that:1) The average TN concentration in wastewater decreased from 122.85 mg·L-1 to 13.48 mg·L-1 after treatment with disturbed soil, and the removal efficiency was 89.03%; and that decreased from 122.85 mg·L-1 to 21.81 mg·L-1 after treatment with undisturbed soil, and the removal efficiency was 82.25%. Disturbed soil increased TN removal efficiency significantly.2) The average nitrogen content of soil was 1.037g·kg-1 before treatment, and that of disturbed and undisturbed soils were 0.820 and 0.915 g·kg-1 after treatment. They had decreased by 0.217 and 0.122 g·kg-1. During the experiment, the fate of nitrogen were atmosphere and deep layer soil n groundwater, so the loss of nitrogen in disturbed and undisturbed soils were 0.326 and 0.223 g·kg-1, respectively.3) The average temperature were 22 and 14 during the experiment in September and ℃October, and the TN Removal efficiencies of disturbed and undisturbed soils in September were 12.60% and 15.89% higher than those in October, respectively. It indicated that temperature has a great effect on TN removal efficiency in soil treating dairy wastewater and low temperature is disadvantageous to it.Due to the limitation of time and conditions, this topic still have some problems worth to be further studied and discussed.(1) This paper studied the influence of freezing and thawing on soil water content, soil grain size distribution, soil porosity and so on, but that on soil mechanics properties and the mechanism of changing the soil structure, still need in-depth study and discussion.(2) In the research, the largest water-soil weight ratio of treating dairy wastewater was obtained according to the experimental data and theoretical analysis. On this basis, whether it is possible the soil particles don’t move if we increase the quantity of dairy wastewater. This hypothesis needs to be tested.(3) In this research, the disturbance of soil can improve the TN removal efficiency of treating dairy wastewater, but more research need to do to confirm whether the degree of soil disturbance has an impact on the removal efficiency.