Suchergebnisse

AbstractIt is estimated that up to 342 wastewater treatment plants (Wwtps) in England and Wales will require a phosphorus (P) consent by 2010. Although biological P removal is considered to be the most sustainable option for P removal, it has always been problematic for plants that remove both nitrogen and P due to the inadequate concentration of organic material during wet periods. Two biological nutrient removal (BNR) configurations, the Johannesburg (JHB) process and a combined JHB and five‐stage Bardenpho process, were evaluated over a period of 2 years to assess the impact of sewage strength on bio‐P removal. The JHB achieved an average effluent total phosphorus (TP) of 2.4 mg/L and the combined JHB and five‐stage process averaged 1.4 mg/L effluent TP. The major problems affecting the performance of both configurations were: dissolved oxygen (DO) in the recycled mixed liquor, nitrate in the return activated sludge (RAS) and low influent biological oxygen demand (BOD) concentrations. Acetate dosing proved successful as a source of volatile fatty acids (VFAs) in the anaerobic zone during periods of low‐strength sewage. An acetate dosing strategy based on the influent flow rate to the plant was found to be a simple and effective technique that ensured that a consent of <1 mg TP/L could be met.

ABSTRACTSludges from two pilot‐scale nutrient‐removal activated‐sludge plants (a modified three‐stage Bardenpho process and a Phostrip plant) were analysed and the results examined, primarily, in relation to the formation of stable foam. The survey showed that both units produced stable foam, but this did not appear to be related either to temperature or to the more conventional operational parameters (sludge age, F:M ratio). The dominance of the sludge by Microthrix parvicella was related to the amount of uronic acids in the extracellular polymers produced by the sludge. The results also indicated that (a) the addition of fermenter elutrient, which was used to produce supplementary readily degradable COD, stimulated foam formation, and (b) the degree of phosphorus removal might also be implicated in the production of foam – and requires further scrutiny.

AbstractThis paper describes a soil‐incubation study which was carried out to examine the effects of (a) phosphorus removal during the treatment of domestic sewage and (b) treating sewage sludge to an enhanced status, on the phosphorus fertiliser value of biosolids which are used in agriculture. Phosphorus‐enriched and conventional dewatered digested biosolids, thermally‐dried pellets and granules, and digested and thermally‐hydrolysed liquid sludges were incorporated into two soil types with contrasting physico‐chemical properties. Plant‐available phosphorus in soil was assessed after incubation by a standard chemical‐extraction procedure. Sludge from biological‐P removal had the highest phosphorus extract‐ability in soil whereas iron dosing slightly reduced or had no effect on phosphorus release from conventionally‐treated biosolids, depending upon the type of soil. High‐temperature drying significantly reduced the extractable‐P content in sludge by 20–60%, compared with dewatered digested cake, and release from thermally‐dried biosolids declined further with iron enrichment. Extractable‐P recovery was greater from all types of biosolids when mixed with calcareous soil, compared with a loamy sand. A preliminary investigation of phosphorus mineralogy in biosolids, using advanced analytical techniques, is also described.