Study On Technologies For Treatment Of High Algae And Organic Matter Polluted Souree Water

The traditional water treatment process is faced with severe challenge from the accelerated pollution of drinking source water. Water quality becomes the key factor for the safety of urban water supply. The water quality characteristics of different kinds of polluted reservoirs were studied in this paper, and some new technologies and processes of source water quality improvement; conventional process enforcement and advanced treatment were proposed and discussed. The followings were the major study and results.1. Such indexes as COD_Mn,TN, TP, NH₃-N, NO₃-N, VOCs, semi VOC_S, odor and algae show that both the mountain reservoir and Yellow River reservoir are polluted by organic matter and algae which cause apparent unpleasant smell. High concentrations of algae and organic matter are the common charicteristics.2. Analysis data showed the current conventional water treatment process has severe shortcomings for treating water polluted by organic matter and algae:The ability of removing algae is limited. The general removal rate of external cellular microcystins is about 28% while the removal rate of total microcystins is about 62%.Odor can hardly be removed through the current process. The major substance causing odor is GSM (geosmin) for treated mountain reservoir water, and is GSM and MIB for the treated Yellow River reservoir water. The concentrations of the odor substances exceeded the corresponding national standards.THMs of the tap water exceeded the national standard, which indicates that the DBPs pollution becomes a big issue while Cl₂ is commonly used for disinfection.3. There is an activated zone in the shallow type reservoir that changes along with the seasonal variations. Ample hydraulic retention time and substrate sludge supplying endogenous N&P nutrition at the bottom of reservoir were the indispensably essential conditions for the activated area to form.4. Based on the research on activated zone, some engineering measures to compress or remove the activated zone would reduce the concentrations of TN&TP, inhibit the excessive multiplication of algae in the water therefore improve the quality of water being drawn from the reservoir for drinking source water. Avoiding the activated area when drawing water from the reservoirs is proposed as a measure to improve the water quality for drinking water source. DDDMAC is a new kind of polymeric flocculant with coco gum as raw materials. Good results were generated on inhibiting algae growth when 1mg/L DDDMAC was added in the water. Therefore it may be used for inhibiting the growth of the algae in the source water in pipeline and that in the water purification units of the water plants.5. The characteristics of the cell breakage of cyanobacterium (M.aeruginosa) during the water treatment process respectively were investigated, and the results showed that coagulation would not cause algae cell breakage, but it would cause intracellular microcystins release in water process. Cl₂ as oxidant may cause both algae cell breakage and intracellular microcystins release.6. Both experimental and on site research showed that either potassium permanganate (KMnO₄) or wet activated powder carbon (WPAC) could remove algae and improve coagulation. KP process in which 0.5mg/L KMnO₄ and 20mg/L WPAC are added in the water at different location, could remove pollutants from algae and odor substance effectively so that the treatment effect of the conventional process was enhanced greatly.7. RemA is designed in the research and the experimental data showed it is a kind of high efficiency coagulant that could remove algae in the polluted reservoir water without breaking the algae cell. More than 90 percent of algae could be removed in the intensified coagulation process with RemA as coagulant. The COD_Mni in the effluent was below 3mg/L and the pollutants of odor were also removed.8. Floating filter tank is set up and the experimental data showed that it is an efficient unit for the treatment of water with high algae concentration. Preoxidation could improve the treatment effect of the floating filter tank greatly and expand its use for different source water as well. The removal rates of all the indexes except COD_Mn were close to or even higher than 90 percent, some of them are even as high as 100 percent. This study would provide technical support for the water plant to find an more effective and safer water purification process.