Application Of Bioleaching Combined With Struvite Crystallization In Phosphorus Recovery From Excess Sludge

At present,most wastewater treatment plants use biological phosphorus removal process,resulting in a large number of phosphorus rich excess activated sludge.Phosphorus is not only a non renewable mineral resource,but also a necessary nutrient element for human beings,animals,plants and other life activities.How to release and recover phosphorus from phosphorus rich sludge is an urgent environmental hot issue,and an effective way to solve the current "phosphorus deficiency" and "phosphorus pollution".In this paper,the effect of bioleaching of Thiobacillus acidophilus on phosphorus release from sludge was discussed.Combined with struvite crystallization method,the released phosphorus was separated and recovered,and the preliminary economic feasibility of bioleaching combined with struvite crystallization for phosphorus recovery from sludge was evaluated,aiming to provide technical reference for efficient recovery of phosphorus resources in sludge.The main results are as follows:(1)Study on the effect of bioleaching by different Acidithiobacillus acidophilus on phosphorus release from sludgeThe bioleaching of Thiobacillus acidophilus can promote the release of phosphorus in sludge.Under the condition of 6 g/L powdered sulfur as energy source and 10% Thiobacillus thiooxidans inoculation ratio,the p H value of sludge decreased significantly after 8 days of treatment,and the total phosphorus content in supernatant reached 430 mg/L and the release amount reached 63.2%.The effect was better than that of single inoculation of Thiobacillus ferrooxidans and combined inoculation of Thiobacillus ferrooxidans and Thiobacillus thiooxidans.And the effect of phosphorus release is related to p H and redox potential,but p H has more influence on phosphorus release.At the same time,it was found that bioleaching promoted the conversion of non apatite inorganic phosphorus to water-soluble phosphate in sludge solid phase,which was the main reason for the release of phosphorus in sludge.(2)Process optimization of phosphorus recovery from phosphorus rich sludge filtrate by struvite crystallizationThe method of struvite crystallization can be used to recover phosphorus released from solid phase of sludge,but the impurities metal cations and DOM in the filtrate have an effect on the recovery of phosphorus by struvite crystallization.The phosphorus rich filtrate was pretreated by cation exchange resin(CER),under the conditions of N: Mg: P molar ratio of 5:1.5:1 and p H of 9.5,the phosphorus recovery was 50.4%,and the purity of struvite was increased from 1.2% to 28.3%;After further ultrafiltration of the sludge filtrate with molecular weight of 10 K Da,the recovery of phosphorus was increased to 59.5%,and the purity of struvite was increased to 37.4%,indicating that a large amount of DOM in the sludge filtrate had a negative impact on the formation and purity of struvite crystals.(3)Economic and technical evaluation of phosphorus recovery from excess sludge by bioleaching combined with struvite crystallizationThe combined process of bioleaching and struvite crystallization for phosphorus recovery from sewage sludge is feasible in terms of economic and environmental benefits.Based on the experimental data,the economic and technical evaluation of bioleaching combined with struvite crystallization process for treating a certain scale of sludge(based on the daily treatment capacity of 500 L sludge)was carried out.It is found that under the existing data conditions,the chemical cost of the combined process is 1898 yuan per year,and the economic value of struvite product is 876 yuan per year.This indicates that the combined process of bioleaching and struvite crystallization is economically feasible for the recovery of phosphorus from municipal sludge,which should be further studied in the future.