Minimization of energy demand in slaughterhouses: Estimated production of biogas generated from the effluent

Many studies have evaluated agroindustrial effluent treatment systems. However, the use of quality control tools in this area is still not widespread, while reports of the use of such tools to monitor slaughterhouse waste treatment systems are practically non-existent. Investigation of exploitation of the energy potential of waste produced within these industries is a strategically important issue, considering the current drive to minimize environmental impacts and to generate power from renewable sources. Therefore, the purpose of this study was to monitor the biological treatment of effluents, using control charts, as well as to estimate the potential production of methane and biogas in a slaughterhouse in southern Brazil. Wastewater samples were collected weekly and measurements were made of ambient and liquid temperatures, pH, solids (total and volatile), chemical oxygen demand (COD), oils and greases (OG), nitrogen, and phosphorus. The potential for methane and biogas production was estimated using the average daily effluent flow rate and the average organic load removal in the anaerobic pond. The effluent treatment system was evaluated by means of the construction of control charts, using the measured variables. This enabled the identification of factors that influenced the effluent treatment process, such as changes in the affluent load, environmental conditions, waste characteristics, and mechanical and human parameters. In terms of energy potential, the use of a covered pond (biodigester) would partially meet the energy demand of the industry, which consumed approximately 66 m(3) of firewood per month, hence requiring 42969 m(3) of biogas per month to supply all its needs. According to theoretical data, the waste could generate around 6790 m(3) of biogas, which would supply 16% of the energy demand, besides providing environmental advantages such as improved efficiency of the treatment system and reduced emissions of greenhouse gases.