Impact of aluminum chloride on process performance and microbial community structure of granular sludge in an upflow anaerobic sludge blanket reactor for natural rubber processing wastewater treatment

Abstract

In this study, granular sludge formation was carried out using an aluminum chloride supplement in an upflow anaerobic sludge blanket (UASB) reactor treating natural rubber processing wastewater. Results show that during the first 75 days after the start-up of the UASB reactor with an organic loading rate (OLR) of 2.65 kg-COD·m(-3)·day(-1), it performed stably with a removal of 90% of the total chemical oxygen demand (COD) and sludge still remained in small dispersed flocs. However, after aluminum chloride was added at a concentration of 300 mg·L(-1) and the OLR range was increased up to 5.32 kg-COD·m(-3)·day(-1), the total COD removal efficiency rose to 96.5 ± 2.6%, with a methane recovery rate of 84.9 ± 13.4%, and the flocs began to form granules. Massively parallel 16S rRNA gene sequencing of the sludge retained in the UASB reactor showed that total sequence reads of Methanosaeta sp. and Methanosarcina sp., reported to be the key organisms for granulation, increased after 311 days of operation. This indicates that the microbial community structure of the retained sludge in the UASB reactor at the end of the experiment gave a good account of itself in not only COD removal, but also granule formation.

Anaerobic Baffled Reactor in Treatment of Natural Rubber Processing Wastewater: Reactor Performance and Analysis of Microbial Community

“…The capacity of the ABR for TSS removal was greater than that of the UASB reactor. Nguyen et al have reported the influent and effluent TSS concentrations of 279 ± 128 mg/L and 72.4 ± 58.5 mg/L, respectively, using the UASB reactor for treating wastewater [6]. On the other hand, the influent and effluent TSS concentrations of 225 ± 125 mg/L and 43 ± 25 mg/L, respectively, were obtained for the ABR in this study.…”

“…The methane recovery ratio based on the total COD removal was 52.4 ± 33.6% during phase 2, while the removal efficiency for total COD in the form of methane improved to 81.3 ± 14.3% using the UASB reactor treating the same type of wastewater [6]. The maximum methane gas production of 29.8 NL/day was observed on the 177th day.…”

“…Recently, UASB and ABR are the frequently used anaerobic process for the treatment of wastewater from natural rubber processing. Some laboratory-scale UASB reactors achieved a high organic removal efficiency and methane recovery rate [5,6]. However, the pilot-scale UASB reactor requires the pretreatment of wastewater because raw wastewater contains high concentrations of sulfate or residual natural rubber particles [7,12].…”

“…Although the UASB reactor has demonstrated excellent performance and stability for numerous full-scale operations worldwide, some obstacles have been observed for its application in treating high concentration of suspended solid wastewater [3]. A considerable amount of residual rubber particles is present in this wastewater, thus a pre-treatment process is required, which can prevent rubber particles from accumulating and clogging pipes and machinery during long-term operation [4][5][6][7]. In addition, the performance of single-configuration reactors considerably depends on the sludge retention capacity, which needs a long start-up period to form granular sludge from dispersed sludge.…”

“…Laboratory-scale [7,9] and pilot-scale [10,11] studies on the use of ABR for the treatment of natural rubber processing wastewater have been reported. However, different profiles of the wastewater discharged from natural rubber processing are observed because of the chemicals used during the coagulation of rubber latex, for example, sulfuric acid [9,12] or organic acids [6,7] in Thailand or Vietnam, respectively. As a result, ABR treated natural rubber processing wastewater in each country exhibits different performances and characteristics.…”