Performance of an UASB Reactor at Lab-Scale Treating Domestic Wastewater with Low Concentrations of Copper

Abstract

Aims: The objective was to investigate the effect of copper at low concentrations in an Upflow Anaerobic Sludge Blanket (UASB) reactor performance under continuous conditions and its geochemical distribution in anaerobic sludge through sequential extraction. Study Design: Continuous operation. Place and Duration of Study: Department of Basic Science, Universidad Autónoma Metropolitana -Azcapotzalco, between July 2013 and December 2013. Methodology: A lab scale UASB reactor was inoculated with sludge from a full-scale UASB reactor treating brewery wastewater and it was allowed to acclimate during two months. After acclimation period, three different copper concentrations were added to UASB influent: 0.25, 0.65 and 1.35 mg l-1, during one month each one. At the end of the experiment, freeze-dried samples of inoculum and UASB reactor sludge were treated with a series of solvents to perform sequential extractions. pH, temperature, oxidation reduction potential (ORP), total chemical oxygen demand (COD), the ratio between partial and total alkalinity, total suspended solids and volatile suspended solids were measured in UASB reactor influent and effluent. Results: Sequential extractions showed that the fraction with the major affinity with copper was organic/sulfide bound, with a percentage distribution of 96%. Regarding UASB performance, copper caused a total alkalinity diminution in the effluent; however, the system buffer capacity was enough to overcome such instability, as partial alkalinity/total alkalinity ratio results confirmed. COD removal decreased 15% when 1.35 mg l-1 Cu was added in comparison to acclimation period. Conclusion: Copper addition in UASB reactor influent at low concentrations affected adversely its performance; though, did not cause complete inhibition to anaerobic microorganisms. Metal speciation results in the inoculum and the UASB reactor evidenced that the fraction which had the major affinity with copper was the organically/sulfide bound fraction, however, further studies are needed to establish which is the weight of organic matter and sulfide in copper binding.