RESEARCH ON SAFETY TEST OF SLUDGE WATER REFLUX COAGULATION

Using lake water in the campus as the raw water, the pilot-scale test of sludge water reflux is conducted to determine the turbidity, chroma, CODMn, UV254, ammonia nitrogen content, total phosphorus content, metal content (Al, Fe, Mn, etc.), total bacterial count and the number of fecal coliform of the water firstly to evaluate the safety of the reflux; then Zeta potential and floe particle size change of the water is measured to indicate the effect of sludge water reflux; finally, the effect for sludge water reflux to treat the low temperature and low turbidity water is investigated. The experiment demonstrates that: under the test conditions, the lowest turbidity and chroma of the effluent appear at a dosage of 30 mg/L, and the reflux ratio is between 2% and 4%; CODMn and UV254 reach the lowest value at reflux ratios of 4% and 6% respectively, with the removal rate increased by 15% - 20%, compared with that without reflux; the ammonia nitrogen content will increase along with the reflux ratio, with the reflux ratio controlled at about 2%; the total phosphorus content is controlled at about 0.4 |ig/L under 2% reflux ratio; the content of Al, Fe, and Mn in the effluent has not accumulated; the total bacterial count and the number of fecal coliforms may be prevented from overgrowth with the reflux ratio controlled within 4%. To sum up, sludge water reflux with an appropriate reflux ratio may guarantee both the enhanced coagulation and the safety of the effluent. Secondly, the FCD floe displayer shows that sludge water reflux can enhance the compactness of the floe with the effect of enhanced coagulation. Finally, the comparison test of the low-temperature and low-turbidity water in the presence or absence of reflux shows that compared with the case of no reflux, the sludge water reflux can increase turbidity and promote CODmh, UV254, and removal rate by 13%, 11%, and 7% respectively.