to obtain a specific per cent removal decreases. Individual tests at Two Rivers, for a broad range of influent phosphorus concentrations, also showed the same variation. Influent total phosphorus ranged from 7.6 to 28.5 mg/l, and the Al:P weight ratios necessary to remove 85% ranged from 2.0:1 to 0.58:1, respectively.

A study of alum addition for phosphorus removal was conducted at Lebanon, Ohio on both pilot and plant scales (11) to determine whether chemical treatment of raw wastewater could be used successfully to precede activated carbon adsorption for organic removal.

A 15 gpm pilot plant was utilized to determine the most effective dosages of alum to be studied in the full-scale tests. Data from the pilot plant indicated that liquid alum dosages of 150, 250, and 350 mg/1, as Al2(SO4)3.14H2O, and anionic polymer dosages of 0.25 and 0.5 mg/1 should be evaluated. Only the Parshall flume, preaeration basin, and primary clarifiers of the 1.5 mgd Lebanon plant were used in this study. Alum was fed to the raw wastewater at the Parshall flume to assure complete mixing. The preaeration basin was used for flocculation, with polymer being added toward the end of the basin. The primary basins served as settlers for the precipitated phosphorus. Figure 4-1 shows the chemical addition arrangement at Lebanon which was used for both alum and iron studies. The iron experiments will be covered later in this chapter.

Each dosage was evaluated for five days. A polymer dose of 0.5 mg/1 was found to be satisfactory for improving floc formation and settling. An alum dose of 250 mg/1, Al:P weight ratio of 3.4:1 (molar ratio of 3.9:1), removed 93% of the phosphorus in this high alkalinity (400 mg/1 as CaCO3) wastewater. Effluent phosphorus concentration did not exceed 0.7 mg/1 and averaged 0.5 mg/1. The alum dose of 150 mg/1, Al:P weight ratio of 1.5:1 (molar ratio of 1.7:1), removed only 74% of the phosphorus; while the alum dose of 350 mg/1, Al:P weight ratio of 3.9:1 (molar ratio of 4.5:1), reduced the phosphorus by 94%. The alum dose needed to meet the State removal requirement of 80% would fall between the 150 and 250 mg/1 dosages studied.

Little data are available for sludges resulting from alum addition to primary settlers. At Lebanon, Ohio, the primary sludge produced by alum addition received lime treatment before final disposal as landfill or on farm land (12). Before lime treatment, the sludge was similar in character to biological sludge and had a solids concentration of from 2 to 3%. It had very poor settling and thickening characteristics and was malodorous.

Lime treatment consisted of mixing the sludge with a 25% lime slurry until a pH of 11.5 was reached. The average lime requirement was 440 lb of lime as Ca(OH)2 per ton of dry solids. A contact time of 30 minutes was maintained before the sludge was allowed to flow to sand beds for drying. Seventy per cent of the total volume of sludge applied to the drying beds was removed as drainage in the first 3 days, and the sludge cake could be lifted off the beds in 3 weeks. Elimination of odors and

complete pathogen kill was accomplished with lime treatment. Lime costs at $18/ton for Ca(OH)2, and an application rate of 440 lb/ton of dry solids, resulted in a chemical cost for sludge handling of $3.96/ton of dry sludge solids.

4.3 Phosphorus Removal Data for Iron Addition

A number of studies have been conducted using the addition of iron to raw wastewater for phosphorus removal. These investigations have ranged from laboratory jar testing to full plant-scale work and have included both ferrous and ferric salts as the source of iron. Average values for doses, phosphorus removals, and references to the studies are listed in Table 4-1.

These studies include wastewaters with phosphorus, concentrations of 6 to 9 mg/1, so a range of phosphorus removals would be expected. In addition, there are many other significant variations in wastewater character from location to location. The results of the studies allow bracketing the phosphorus removals obtained and enable drawing conclusions based on special features of individual studies.

With primary treatment alone, phosphorus removals varied from 60 to 91%. In secondary plants, iron addition before the primary resulted in phosphorus removals from 75 to 93% over the entire plant. Iron doses varied between 10 and 90 mg/1, as Fe. The Escanaba study showed that base and polymer addition could halve the iron dose required to obtain the same phosphorus removal achieved with iron alone. The Lebanon study showed that doubling the iron dose (from 45 to 90 mg/1) with the same polymer addition raised phosphorus removal from 68 to 91%. At Wyoming, Michigan, the same phosphorus removal was obtained with equal doses of either Fe2+ or Fe3+. Polymer doses in all of the iron studies ranged from 0.26 to 0.7 mg/1.

Iron carry-over occurred at Mentor, where FeCl2 addition alone resulted in an effluent Fe concentration of 42.5 mg/1. Lime addition reduced the iron leakage to an effluent Fe concentration of 11.6 mg/1. Polymers were ineffective in reducing iron leakage.

Increased suspended solids and BOD removals were also obtained with iron additions. At Grayling, Michigan, suspended solids removal was increased by 27% to an average of 78%. At Benton Harbor, Michigan, where waste activated sludge is returned to the primary, iron addition gave a 3.0% increase in solids removal over the entire treatment plant. An example of increased BOD removal is seen in the Grayling, Michigan study. Removal of BOD in the primary was increased by 45% after iron addition. This resulted in a total BOD removal of 58% in the primary.

Typical values for primary settler detention times were 2.3 hours at Mentor and 2.25 hours at Benton Harbor. At Mentor, air at a rate of 42.5 to 85 ft/minute was used for flocculation in the mixing area of the primary tank.

Although lab test procedures should be adjusted to best approximate individual plant conditions, outlines of procedures used at two locations may be useful as guidelines. Jar tests were conducted at Mentor in the following manner. Iron, lime, and polymer