Fraction Of Municipal Sewage Sludge Research Articles

Phosphorus recovery as struvite and hydroxyapatite from the liquid fraction of municipal sewage sludge with limited magnesium addition.

Phosphorus (P) is an essential element to produce feed and fertilizers but also a nonrenewable resource. Both the predicted exhaustion of phosphatic rocks and the risk of eutrophication lead to an increasing necessity for P recovery methodologies to be applied in municipal wastewater treatment plants (WWTPs). One of the most promising solutions involves the precipitation of P-based minerals reusable as slow-release fertilizers. In this study, P recovery as struvite and hydroxyapatite from a municipal WWTP digestate liquid fraction (centrate) was investigated at varying pH (8-10), reagent typologies (MgCl2 , NaOH, Ca(OH)2 , and CaCl2 ), and concentrations under limiting magnesium doses through liquid- and solid-phase analyses and thermodynamical modeling. A maximum P recovery of 87.3% was achieved at pH 9 by adding NaOH and MgCl2 at a dose of 656mg/L (the higher tested). According to these data, it was estimated that 92.0 tons/year of struvite and 33.2 tons/year of hydroxyapatite could be recovered from the WWTP centrate with a cost for reagent consumption being almost 50% of the mean P market value. An increase in P precipitation was observed while comparing experiments with the same pH values but with a higher Mg2+ dose. Ca2+ addition led to extensive P precipitation but mainly as amorphous phases that interfere with struvite formation.

Cinétique de biolixiviation d'un résidu minier de pyrite en présence d'effluents organiques utilisés comme milieu de culture pour Acidithiobacillus ferrooxidans

In this study, the results of the leaching of metal sulphide concentrate using organic wastes as culture media for Acidithiobacillus ferrooxidans are summarized. These results indicate that the liquid fraction of municipal sewage sludge, paper mill sludge and pig manure, containing 10 % (w v−1) pulp density of a pyritic mine waste concentrate can support the growth of the leaching bacteria and allow metal solubilization. The inhibition by dissolved organic carbon (DOC) appeared when the concentration in pig manure liquid fraction and sewage sludge filtrate is higher than 180 mg 1−1 and 500 mg l−1, respectively. However, increase in organic concentration up to 650 mg l−1 using paper mill sludge supernatant had no inhibitory effect on the bacterial growth. An important decrease of the DOC has been measured during all bioleaching tests. The organic matter was probably consumed by heterotrophic microorganisms activity. The growth rate of the iron‐oxidizing bacteria varied from 0.05 to 0.07 h−1. The dissolution of pyrite (FeS2) in organic waste media led to a yield of Fe solubilization of about 35 %. Copper and zinc were also solubilized during the bioleaching tests. The yields of Cu and Zn solubilization ranged from 12 to 24 %.

Wastewater sludge and pig manure used as culture media for bioleaching of metal sulphides

Precious and base metal recovery from leaching metal sulphide concentrates or low-grade ores is often based on the activity of bacteria, mainly Acidithiobacillus ferrooxidans, which converts insoluble metal sulphides into soluble sulphates. This study explored the possibility of using organic wastes as nutrients during the growth of A. ferrooxidans. Flask bioleaching tests using 10% (v/v) pulp density of a pyritic mine waste concentrate have shown that the liquid fraction of municipal sewage sludge, paper mill sludge and pig manure can support the growth of the leaching bacteria and allow metal solubilisation almost like a synthetic mineral medium. Dilution of these organic wastes is required to reduce the dissolved organic carbon (DOC) concentration, which inhibited the bacterial growth activity. The toxicity of the DOC appeared when the concentration of pig manure supernatant and sewage sludge filtrate was higher than 180 and 500 mg/L, respectively. A lag period has been noted before the active growth of A. ferrooxidans in the presence of pig manure and sewage sludge. In contrast to sewage sludge and pig manure, there is no toxicity detected (no bacterial activity inhibition and lag phase period), using paper mill sludge supernatant containing DOC ranging from 40 to 350 mg/L. An important decrease of the DOC (23–94%) has been measured during all bioleaching tests. The organic matter was probably removed by heterotrophic microorganism activity.