Browsing by Author "Sakeus, Kafula"

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    Anaerobic digestion of dairy manure wastewater, food and fruit waste, a sustainable source of bio-energy and waste management
    (Stellenbosch : Stellenbosch University, 2016-03) Sakeus, Kafula; Lotze, Elmi; Raffrenato, Emiliano; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The potential for anaerobic co-digestion (AD) organic waste streams such as dairy manure waste water, fruit and food waste is a well-established process. A pilot study, utilizing a new constructed 40.248 m3 plug-flow, three chamber anaerobic reactor was conducted to determine the effects of temperature, electrical conductivity (EC), pH, organic loading rate (OLR) over a 20 day hydraulic retention time (HRT) on biogas yield, waste volume reduction, water soluble minerals, reduction of pathogenic microorganisms (Escherichia coli O157:H7), phytotoxcity and anaerobic microbial population dynamics. The reactor was equipped with a build-in temperature sensor which allowed for the internal temperature to be recorded from the circulation of water via an 8L biogas geyser. The reactor was also fitted with three ports connected to the three individual chambers, from which samples for EC and pH were lifted for analysis. Dairy manure wastewater had a total soluble (TSS) concentration (2.59 g/l) which was considerably lower than the anticipated 10% TSS. This meant the reactor had an OLR of 2.59 kg/m3reactor/day (Total suspended solids) and 1.97 kg/m3reactor/day volatile suspended solids (VSS). To maintain an organic retention time (ORT) equivalent to HRT, co-digestion of fruit and food waste was than calculated based on the TSS and VSS content of dairy manure wastewater. The results validated that the reactor’s temperature plays an important role in the production of biogas and reduction of pathogenic microorganisms of the digestate. Due to the low temperatures during the trial period, no viable biogas yields were detected using the current water displacement system and thus no biogas quality analysis were conducted. Temperature data confirmed that at temperatures below 20 °C, there was no linear relationship between the salinity indicator, EC and temperature. In addition, these low psychrophilic temperatures at a HRT of 20 days had no comparable impact on the reduction of pathogenic microorganisms. However, a 97% reduction in TSS entering the reactor was observed in all digestates. Water soluble minerals entering the reactor through feedstock were comparable to the soluble mineral concentrations the digestate. Although, the digestates contained high concentrations of mineral nutrients such as ammonium which were above the legal limit of waste water to be discharged in the environment. At concentrations below 75% none of the digestates showed significant phytotoxicity effects quantified with tomato seed germination. While, the data also seem to suggest that OLR had a noticeable influence on microbial population dynamics. Overfeeding the reactor induced an instant decreased on pH and also increased the microbial population species that colonize the different chambers. Under current sub-operating conditions compounded by low OLR, the AD reactor was not competitive enough to replace the current composting operation.