Wastewater phosphate removal

Single-strand conformation polymorphism (SSCP) Wastewater bioreactors (including denitrifying and phosphate-removal system, Chinese traditional medicine wastewater treatment system, beer wastewater treatment system, fermentative biohydrogen producing system, and sulfate-reduction system) Microbial community structures, diversity and distribution in different wastewater treatment processes, and relationship between the structures and the status of processes [157]... 

We have proposed a fluidized bed type process, which can be applied to phosphate removal from wastewater containing phosphate 2-23 mg/jg as P.By the results of experiments using equipment of capacity l-4m3 /day, factors such as supersaturation, recirculation ratio and space velocity were recognized to affect crystallization rate or phosphate removal efficiency. By mathematical analysis, we could obtain the characteristic equation for fluidized bed process, to agree well with experimental results. 

Phosphate removal processes from wastewater have been studied by many workers, in order to protect stagnant water area, such as lakes and coastal region from eutrophication. Among conventional phosphate removal processes, the representative one was flocculation and sedimentation process, which was based on precipitation of insoluble metal phosphate or hydroxide. However, the main problem with this process, is to produce large amounts of sludge, which is difficult to dehydrate. 

To cope with these problems, we have developed phosphate removal process using crystallization, which can minimize the amount of sludge and recover phosphate. Mechanism of this process is crystallization of calcium phosphate on the surface of phosphate rocks by contacting supersaturated solution with them. In case of application to wastewater containing 1-3 mg/jg phosphate as P, we proposed fixed bed type process, which has demonstrated excellent performance in the sewage treatment. 

Table 1 shows the performance of fixed bed type process, in application to various wastewaters. The merit of this process is stability in ability of phosphate removal and low sludge production. Sludge production of this process is from 1/5 to 1/10 lower than that of the conventional flocculation and sedimentation process. 

We have now proposed fluidized bed type process, which can be applied to wastewater, containing from 2 to 23 mg/jg phosphate as P. This report reveals fundamental studies on factors affecting phosphate removal and crystallization rate in the fluidized bed process. 

Figure 1 shows the schematic illustration of phosphate removal mechanism. Phosphate in wastewater contacts with seeds made of phosphate rock, after chemical conditioning such as supply of calcium and hydroxide ion. Then calcium phosphate, mainly hydroxyapatite, crystallizes, according to eq.(l), on the surface of phosphate rocks. 

We have reported only the results of the last investigation of fundamental properties of this process. But there are many problems remaining unsolved such as growing mechanism of calcium phosphate, the reason of difference in phosphate removal efficiency between application to wastewater and tap water, and also how contaminants include into growing calcium phosphate. 

J. W. McGrath and J. P. Quinn (2003). Microbial phosphate removal and polyphosphate production from wastewaters. Adv. Appl. Microbiol., 52, 75-100. 

T. Mino (2000). Microbial selection of polyphosphate-accumulating bacteria in activated sludge wastewater treatment process for enhanced biological phosphate removal, Biochemistry (Moscow), 65, 541-549. 

Battistoni, P, et al. (1998). Phosphate removal in real anaerobic supernatants Modelling and performance of a fluidized bed reactor. Water Science Technol. Wastewater Nutrient Removal, Proc. 1998 19th Biennial Conf. Int. Assoc, on Water Quality, Part 1, June 21-26, Vancouver, Canada, 38, 1, 275-283. Elsevier Science Ltd. Exeter, England. 

The importance of redox effects on coupled iron-phosphorus cycling in freshwater systems has been the subject of study in applied environmental science, where phosphate removal from eutrophic natural waters and wastewaters, by sorption onto Fe-oxyhydroxide phases, has been explored as a remediation measure. Phosphate also has a pronounced tendency to sorb onto Al-oxyhydroxides, and these phases have been used in remediation of phosphate overenriched aquatic systems, as well (e.g., Leckie and Stumm, 1970). 

Using Eq. 6-37, we can determine Ct.po (= Ct,ai) cts a function of pH. This relationship is plotted in Fig. 6-13. It shows that AlP04(s) has a minimum solubility in the neighborhood of pH 5.5. This information is useful to us because it indicates that it would be inappropriate to attempt AlP04(s> precipitation for phosphate removal from solutions containing in the range of 10 to 10 mole P04/liter (which is typical of wastewaters) at... 

H. L, Recht and M. Ghassemi, "Kinetics and Mechanism of Precipitation and Nature of the Precipitate Obtained in Phosphate Removal from Wastewater Using Aluminum(III) and Iron(III) Salts," Report No. 17010EKI 04/70, U.S. Dept, of Interior, Federal Water Quality Adm., Cincinnati, 1970. 

The addition of diammonium hydrogen phosphate (DAHP) resulted in an increase in PHB production to 67% when raw rice grain-based spentwash was used. The same wastewater after removal of suspended solids by filtration and with DAHP supplementation resulted in lower PHB production (57.9%). Supplementing other wastes with DAHP led to a substantial decrease in PHB content in comparison to what was observed in the absence of DAHP. Such studies indicate the feasibility of using wastewater for PHA production. 

Hard-burned magnesias may be used in a variety of appHcations such as ceramics (qv), animal feed supplements, acid neutralization, wastewater treatment, leather (qv) tanning, magnesium phosphate cements, magnesium compound manufacturing, fertilizer, or as a raw material for fused magnesia. A patented process has introduced this material as a cation adsorbent for metals removal in wastewater treatment (132). 

Sodium alumiaate is an effective precipitant for soluble phosphate ia sewage and is especially useful ia wastewater having low alkaliaity (20,21). Sodium alumiaate hydrolyzes ia water to Al(OH)2 and Al" which precipitate soluble phosphate as aluminum phosphate [7784-30-7], AlPO. Sodium alumiaate has also been described as an effective aid for the removal of fluorides from some iadustrial waste waters (22). Combiaations of sodium alumiaate and other chemicals are being used to improve the detackification of paint particles ia water from spray-painting operations (23). 

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