Study On The Decentralized Rural Domestic Wastewater Land Treatment Systems

Rural domestic wastewaters, the main source caused serious river and lake pollution, were always discharged into the rivers and lakes around the rural residences directly. It’s significant for rural pollution controlling and rural environment protection to select the land treatment technologies which were cost-effective, no need of mechanical equipment and simplicity of operation and maintenance.This research was about the issues of rural domestic wastewater and wastewater land treatment system based on the bench-scall and field-scall experiment. On the basis of bibliometric analysis on wastewater research, the trend of wastewater research was studied. The equilibrium adsorption data of phosphorus onto red soil were analyzed and non-linear regression was used to determine the best-fitting isotherm. High efficient pollutant-degrading bacteria were isolated from sludge samples. Unplanted filters, which were filled with different filter media, were operated to assess their nutrient removal performances. Two types of decentralized rural domestic wastewater land treatment systems (IST+CMFB+CW, ICW) were studied to assess their performances of nutrient removal. Self-organizing map (SOM) model was also applied into to wastewater land treatment system for water quality real time control.In this study, the issues of wastewater were found by bibliometric analysis, and mechanisms of the land treatment system were studied. Finally, the land treatment technologies were assessed.The main results are as follows:(1) The equilibrium adsorption of phosphate from aqueous solution using red soil was investigated. The linear and non-linear regression were used and compared to determine the best-fitting isotherm. The linear regression method for determining the best-fitting isotherms was not appropriate in this study; the correct method should be non-linear regression. Redlich-Peterson seemed to be the best-fitting isotherms for the experiment results.(2) Filters, which were filled with four types of filter medium (natural zeolite, blast furnace granulated slag, ceramsite, and walnut shells), were operated to assess their nutrient removal performances. Compared with other filters, blast furnace granulated slag-filled filters performed best concerning nutrient removal and retention. Walnut shell-filled filters performed worst. Blast furnace granulated slag was resistant to the pH changes.(3) Preprocessing method involving aerobic and anaerobic sludge was applied to the filters to accelerate the treatment processes. The results indicated that preprocessing enhanced the chemical oxygen demand (COD) removal. Filters containing blast furnace granulated slag were independent with respect to COD loading rate variations in the range between 100 and 900 mg/d, the COD removal rates were between 68% and 81%. A linear velocity equation was used to determine the nutrient removal velocities of blast furnace granulated slag-filled filters. The removal velocities were rapid, and highest for total phosphorus (TP) and lowest for total nitrogen (TN).(4) Four types of high efficient pollutant-degrading bacteria:DWT-2, DWT-4, DWT-6 and DWT-7, were isolated from sludge samples. Based on their morphological, physiological and biochemical characteristics, these bacteria were identified as Alcaligenes sp., Pseudomonas sp., Klebsiella sp. and Pseudomonas sp.. DWT-2 and DWT-4 were identified as highly efficient COD-degrading bacteria, and DWT-6 and DWT-7 were identified as highly efficient phosphorus-degrading bacteria on the basis of bench scale experiments. The performances of three combinations of DWT-2 and DWT-7 with proportions of 2:1,1:1 and 1:2 were relatively good.(5) The combined system IST+CMFB+CW around Lake Dianchi showed relatively good removal efficiency of COD, TP and TN; the effluent pollutants concentrations met the requirement of the agricultural water. The influence of the seasonal variations on the TN and TP removal was not obvious. Compared to other technologies, this system showed high treatment capacity for rural domestic wastewater treatment with good landscape integration. Results demonstrated that this system could be a practical technology for onsite domestic wastewater treatment in rural areas.(6) The removal efficiencies of ICW around annestown valley system were relatively good for soluble reactive phosphorus (SRP), NH4+-N, NO3-N, biochemical oxygen demand (BOD), COD, suspended solids (SS), and E-coli. The water quality was improved by this technology. The outflow water quality met the standards for discharge from wastewater treatment plants in Ireland. The results showed that ICW were likely to be efficient for nutrient removal from rural domestic wastewater rich in nutrients, this system is suitable to be applied in rural area for wastewater pollution control.(7) A self-organizing map (SOM) model was applied as a prediction tool for the performance of an ICW system treating rural domestic wastewater to protect receiving watercourses. The relationships between ICW outflow water quality parameters can be very well visualized by using SOM model. By utilizing the SOM model, the time-consuming to measure expensive BOD outflow concentrations were predicted well by other inexpensive variables, which were quicker and easier to measure. Correct predictions for the outflow biochemical oxygen demand concentrations were high. Moreover, the missing values and outliers from the large but incomplete ICW data set were replaced accurately by most likely values determined by the SOM model. As a prediction method, this approach could be potentially applied in other field-scale land treatment systems.(8) The study indicated that IST+CMFB+CW and ICW, the decentralized land treatment systems, were successfully applied for rural domestic wastewater treatment. The designs of them were based on the holistic use of land and environmental, ecological structure of the landscape to control water quality; they were cost-effective, no need of mechanical equipment and simplicity of operation and maintenance, natural contours around the residences were utilized to support the good distribution of flows in the system. IST+CMFB+CW systems were constructed using various scattered open land spaces around rural residences, little land area was occupied. ICW systems took up relatively large-sized appropriative grounds; this greatly limits the use of those systems for domestic wastewater treatment in China.