Processing organic wastes and returning them ultimately to the land is one 

 of the most far-sighted methods for dealing with them. One of the largest 

 demonstrations of this technique is currently underway at Muskegon, 

 Michigan. 



Another way to reduce the nutrient input is to remove specific nutri- 

 ents by advanced waste treatment. Either nitrogen or phosphorus or both 

 can be removed. One of EPA's current major research undertakings is a 

 unique project to demonstrate the feasibility and dynamics of restoring a 

 deteriorating lake by removing phoshorus from municipal wastewater flowing 

 into it. Shagawa Lake, in northeastern Minnesota, was selected to demon- 

 strate this technique. High inputs of phosphorus supplied by the lake 

 shore city of Ely have caused excessive productivity and undesirable 

 conditions in the lake. Ely, producing at a maximum about 3500 m 3 

 (1,000,000 gal) of wastewater daily, has had a municipal sewer system since 

 1901 and a secondary treatment plant since 1954. The effluent has always 

 been discharged into Shagawa Lake. As a result, over the last 70 years, 

 the lake has become increasingly eutrophic, a condition in great contrast 

 to the near-pristine surrounding lakes. A $2.3 million tertiary waste- 

 treatment facility, designed to remove more than 99% of the phosphorus in 

 the wastewater from the secondary sewage treatment plant, was constructed 

 with 95% financing by EPA. Full-scale operation began in early 1973. 

 Phosphorus is removed by chemical treatment, primarily with lime and lesser 

 amounts of ferric chloride, settling, and filtration. Only about 68 kg of 

 phosphorus now enter the lake each year from this source, instead of the 

 6,800 kg before tertiary treatment. This plant is unique in the United 

 States in removing phosphorus from all of the municipal wastewater to a 

 residual of 0.05 mg/liter. 



According to existing mathematical models of Shagana Lake, recovery 

 should be rapid, very likely reaching a new phosphorus equilibrium in \\ to 

 Th. years. However, when taking into account the phosphorus contained in 

 the bottom sediment, and its exchange with the overlying water, additional 

 time must be allowed for depletion of this nutrient source. Nevertheless, 

 significant reduction in the phosphorus level of lake water has been noted, 

 and the chlorophyll a concentration has been reduced from pre-treatment 

 levels. 



Product Mod if ication-- 



Still another way to limit nutrient loading to lakes is to modify 

 nutrient-rich products to reduce their growth-promoting potential. The 

 best example is phosphorus compounds in detergents. It has been estimated 

 that on a per capita basis 0.96 kg of phosphorus per capita year was 

 utilized in the household and 0.24 kg per capita year was utilized in indus- 

 try (Porcella et al., 1974). 



On the average, roughly half of the phosphates entering U.S. streams 

 come from municipal wastes and urban runoff. The other half comes from 

 natural runoff, industrial and agricultural wastes, and animal feed lots. 

 About half of the phosphates in domestic wastes are of detergent origin 

 (Hatling and Carcich, 1973). Thus, detergents account for about one- 

 quarter of the phosphates discharged into lakes and streams. 



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