Anaerobic treatment of sugarcane vinasse pretreated with a calcium-based biopolymer

Abstract

This study investigated the influence of a previous sugarcane vinasse coagulation, by using a calcium-based biopolymer, on anaerobic treatment in a lab-scale reactor. Two anaerobic reactors (R1 and R2) were operated for 155 days. R1 was fed only with raw sugarcane vinasse and R2 was fed with pretreated effluent. The operation was divided into three stages: E1 (inoculation and adaptation); E2; and E3. The major difference between E2 and E3 was the fact that R2 failed at the end of E2. Thus, R2 was recovered by applying a low organic loading rate (OLR) of raw vinasse for 29 days. In E2 and E3, for both reactors, pH, alkalinity, COD (influent and effluent samples), and methane production were monitored. During E1, an OLR of 2.0 kgCOD. m-3.d-1 1 was applied, and R1 and R2 sludges showed good adaptation to the wastewater in this condition. Then, the OLR was progressively increased to 7.0 kgCOD.m-3.d-1 in both systems. The average COD removal efficiencies were 82.9 ± 4.4% and 72.2 ± 18.1% for R1 and R2, respectively. R2, operated with pretreated vinasse, showed a decrease in the COD removal and methane production, which could be caused by the biopolymer presence. The average COD removal efficiencies in E3 were 77.5 ± 9.4% and 79.2 ± 9.7% for R1 and R2, respectively. After 155 days of operation, a decrease in the COD removal and methane production was identified again in R2, indicating a new failure. The quality of sludge granules from the inoculum and also from the granules developed at the end of R1 and R2 operation was analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). These analyses indicated a rise in the rugosity of R1 and R2 granules, possibly due to the deposition of sedimentable compounds present in both raw and pretreated vinasse. The EDS analyses indicated a high presence of calcium in R2 granules, indicating that this compound acted in the reduction of mass transfer between organic load from vinasse and the granules’ microbiota.