Abstract
Cattle slaughterhouse wastewater (CSWW) with an average chemical oxygen demand (COD) and biochemical oxygen demand of 32,000 mg/L and 17,000 mg/L, respectively, can cause a severe environmental hazard if discharged untreated. Conventional upflow anaerobic sludge blanket (UASB) reactor is used in the treatment of slaughterhouse wastewater to meet the discharge standard limit of wastewater discharge set by the Department of Environment Malaysia (DOE). However, at higher loading rates the conventional systems are characterized by slow-growing microorganism resulting in long startup period, surface scum formation, and sludge washout. In this work, the performance of two laboratory scale (12 L) conventional (R1) and modified (R2) UASB reactors treating CSWW at mesophilic (36 ± 1 °C) condition were investigated. Both reactors were subjected to increasing organic loading rate (OLR) from 1.75 to 32 g L−1 day−1. The average COD, BOD5, and TSS removal efficiencies were ˃90%, at an OLR between 1.75 to 5 g L−1 day−1. The study revealed that R1 drastically reduced to 50, 53, and 43% with increasing OLR until 16 g L−1 day−1, whereas R2 maintained 76, 77, and 88% respectively, under the same OLR. Sign of reactor instability was very much pronounced in R1, showing poorly active Methanosaeta spp., whereas R2 showed a predominantly active Methanosarcina spp.
Highlights
The demand for effective treatment of high-strength industrial wastewater has increased over time, due to the effects related to environmental pollution
The examination of the conventional (R1) and the modified (R2) upflow anaerobic sludge blanket (UASB) reactors demonstrates that both reactors had comparably high chemical oxygen demand (COD) removal efficiencies, being >90% on the average, at a loading rate of 5 g L−1 day −1 corresponding to 10,000 mg/L COD
On further increase of organic load to both reactors, the modified UASB reactor R2 exhibited high organic-matter removal efficiency accompanied by steady performance and shock loading tolerance as compared to R1
Summary
The demand for effective treatment of high-strength industrial wastewater has increased over time, due to the effects related to environmental pollution. Cattle slaughterhouses are among the many food industries that are utilizing a considerable quantity of freshwater and generate a large volume of wastewater rich in organic contaminants and nutrients [1]. Wastewater produced during slaughter and cleaning processes usually consists of the animal fats, blood, urine, feces, soil from hides, soft tissue removed during trimming, and cleaning and sanitizing compounds [2]. Rivers have natural cleansing capacity, Water 2019, 11, 806; doi:10.3390/w11040806 www.mdpi.com/journal/water. Water 2019, 11, 806 the frequent release of such effluent without being adequately treated might overburden the receiving water body. The volume of water consumption per animal slaughtered varies according to the type of animals and the process used. Ahmadian et al [4] and Caixeta et al [5] reported values between
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