A series of experimental investigations was conducted to determine the levels of phosphorus present in municipal wastewater attributed to detergents and their persistence in water bodies. Experiments were also conducted to determine the biodegradability of detergents in water. The study was conducted from September, 1988 to March 1989 and the rivers selected for the study are Pasig and Marikina Rivers.
The preliminary acid-hydrolysis and stannous chloride methods were used to measure the acid hydorlyzable phosphates. Total orthophosphates were analyzed using the stannous chloride method. The detergent concentrations in the river and wastewater effluent were detected by the methylene blue active surfactants (MBAS) method. The data showed that of the total detergent in the wastewater, 12 to 13% are phosphates. This was confirmed by the a parallel analyses of the phosphorus concentration of the different brands of detergents available in the market. The study indicated that 12 to 17% phosphate builders comprise the commercial detergents. Street wastewater, laundry wastewater concentrations were likewise examined. Of the two study rivers, it appeared that Pasig River is more polluted in terms of phosphorus than the Marikina River. A mean value of 0.065 mg/l of acid hydrolazable-phosphate was observed in the whole stretch of the Pasig River, while 0.043 mg/l was recorded for Marikina River. A mean value of the detergents content in Pasig River is 0.485 mg/l; for Marikina River, 0.330 mg/l during the investigation period. The data covers sampling for dry and wet season.
The date gathered were treated statistically. A correlation coefficient, 0.99 using the pearson product moment correlation coefficient was obtained. From the experiments, the range of phosphates in detergents was found to be from 0.006 mg/l - 0.170 mg/l for Pasig River while 0 - 0.138 mg/l for Marikina Rivers system.
Test for biodegradation of selected commercial detergents were conducted in the laboratory to determine their degradation rates. Several factors that affect the rate of biodegradability were considered; bacteria, dissolved oxygen and nutrients. The test for biodegradation of detergent was conducted for a period of two months. Initial concentrations of detergents in the amount of 20 mg/l and 30 mg/l were used. At 20 mg/l, 16% was degraded in a period of 63 days. For samples which were seeded with bacteria, 50% degradation at 63 days was observed. Addition of nutrients, 8 mg/l of potassium nitrate and continuously aerated, resulted in a biodegradation of 50% in 43 days.
One of the problems encountered in the eutrophication of water includes the risk of increased bacterial growth due to the fouling of the distribution networks and nutrient content. Because of the high content of organic substances in eutophied waters and some of the problems (taste, ammonia, regrowth of organisms, etc.) these waters are often extensively chlorinated during treatment as well as in the initial transportation and final distribution networks. High levels of both chlorine and organic substances lead to significant concentrations of organochlorinated compound in water, and these substances are now considered to be potentially hazardous for human health (carcinogenic risk). Water should thus be protected from eutrophication.(Author)