Problem describes the operation of an RBC plant that adds alum to the biodisk effluent to precipitate phosphate in the final clarifiers. Assume that the total phosphorus in the raw unsettled wastewater is 10.1 mg/l, consisting of 3.0 mg/l organic phosphorus and 7.1 mg/l inorganic phosphorus.
(a) Trace phosphorus through the plant from influent to effluent as illustrated in Figure 14.7, and write the appropriate chemical and biological reactions resulting in phosphorus removal.
(b) Calculate the alum dosage in milligrams per liter as alum and as the weight ratio of Al/P. How do these values compare with values given in Section 14.9 under the heading “Chemical Precipitation and Biological Treatment”?
Problem:
A domestic wastewater plant using rotating biological contactors for secondary treatment (Figure 12.30) has a two-stage anaerobic digestion system (Figure 13.13).The first stage is a heated, completely mixed fixed-cover digester with a liquid volume of 15,500 ft3. The second stage is an unheated and unmixed digester with a liquid volume of 15,500 ft3 equipped with a gas-dome cover and supernatant draw-offs. Alum is added to the RBC effluent ahead of the final clarifiers to precipitate phosphate. (The plant was retrofitted with alum feeders and new final clarifiers after original construction to meet a revised effluent standard for phosphorus.) The average wastewater flow is 0.63 mgd. Influent characteristics are 166 mg/l of BOD, 128 mg/l of suspended solids, and 7.1 mg/l of inorganic phosphorus. Effluent characteristics are 7 mg/l of BOD, 16 mg/l of suspended solids, and 1.3 mg/l of inorganic phosphorus. Alum addition is 405 lb/day. The quantity of raw sludge produced averages 7.400 gpd with 4.4% solids, which arc 67% volatile. The quantity of digested sludge accumulated in the second-stage lank averages 1500 gpd with 4.3% solids, which are 45% volatile. The total gas production from digestion is 4200 ft3/day.
(a) Calculate the volatile solids loading and liquid detention time of the first-stage digester. How do these values compare with those in Table 13.8? ,
(b) Calculate the digestion gas production per pound of volatile solids added and per pound of volatile solids destroyed. Compare these values with those in Table 13.6. ,
(c) Estimate the total dry solids sludge yield as the sum of raw primary solids [Eq. (13.5)j, biological sludge solids [Eq. (13.6)]. and alum precipitate as aluminum phosphate [Eq. (14.5)]. How does this compare with actual sludge solids yield?
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