Alum recovery and wastewater sludge stabilization with sulfuric acid

Abstract

Coagulation-flocculation is used to remove helminth ova from wastewater intended for agricultural reuse. Nevertheless, it has the drawback of producing a large amount of sludge which together with the chemicals used to treat the wastewater increases the operating cost. This can be overcome by recovering and recycling the aluminium contained in the sludge. This paper presents how an acid recovery process was applied to an Advanced Primary Treatment (APT) sludge to partially treat it and to reduce its quantity. This is a method applied several decades ago in water sludge that has not been used in secondary wastewater sludge to recover aluminium and to inactivate microorganisms. By adding sulphuric acid to a 6%TS sludge, more than 70% of the aluminium added during the coagulation flocculation process was recovered when a pH of 2 was maintained during 30 minutes and at 300 rpm of mixing conditions. This way the sludge was reduced by 45% in volume and by 63% by mass, inactivating 5 logs of faecal coliforms and 68% of helminth ova. Due to the lower alum consumption, the operating cost of the APT is reduced by 3.78 US$/1,000 m(3).

Coagulant Recovery from Water Treatment Residuals: A Review of Applicable Technologies

“…Addition of acid beyond this solubilized no more aluminum. This is contrary to what might be expected for WW sludge which has higher alkalinity levels (Slechta and Culp, 1967) but was explained by a low WW pH of 5, indicating minimal buffering capacity (Jimenez et al, 2007). The study also found that increased solids above 5.9% in the sludge feed led to reduced recovery efficiencies at the mixing conditions and duration tested.…”

“…As these options become more established, the marginal benefit of recycling coagulants is diminished, potentially making the return on the initial capital investment for CR harder to achieve during its operational lifetime. Bishop et al (1987); c) Chen et al (1976); d) Dymaczewski et al (1997); e) Elliott et al (1990); f) Gallimore et al (1999); g) Georgantas and Grigoropoulou (2005); h) Godbold et al (2003); i) Jimenez et al (2007); j) King et al (1975); k) Lindsey and Tongkasame (1975); l) Petruzzelli et al (2000); m) Pigeon et al (1978); n) Prakash and Sengupta (2004); o) Sengupta (1994) (Zhao et al, 2009). Removals of 73% for chemical oxygen demand (COD), 83% for biological oxygen demand (BOD 5 ), 86% for reactive P, 89% for soluble reactive P, and 78% for suspended solids (SS) were found.…”

“…Alum was recovered from primary WW sludge with a yield of 70% at a pH of 2 (Jimenez et al, 2007). The recovered coagulant not only performed comparably to fresh coagulant (when supplemented with 30% fresh material) but also reduced residual sludge volume and mass by 45% and 63%, respectively.…”

“…The study was only partly successful in its aim to inactivate helminth ova in the insoluble sludge fraction to enable the residual sludge to meet agricultural standards for application to crops for human consumption. For this, further stabilization with lime would be required (Jimenez et al, 2007).…”

k-Value-based ferron assay and its application

“…Moreover, aluminum is a major plant growthlimiting factor in many acid soils; many efforts have been focused on assessment of the relative toxicities of Al species. Considering the increasing interests on Al phytotoxicity and PACl application [19,20], a convenient method for precise speciation based on the rate constant rather than 27 Al NMR is basically required.…”