An evaluation of a laboratory-scale aerobic method for the treatment of potato-processing wastewater at 37°C was investigated. Composite samples were collected to establish batch variations. The wastewater was characterized for Chemical Oxygen Demand (COD), Permanganate Value (PV), Total Solids (TS), phosphates and pH over a period of 6 months. Wastewater with an average of 6.8 g COD/l, high concentration of total solids (up to 6725 mg/l), and low pH was subjected to active sludge treatment in a Continuously Stirred Tank Reactor (CSTR) with Organic Loading Rates (OLRs) gradually increased from 3.4 to 12.1 g COD/litre/day. Stepwise increase in OLR reduced average COD reduction from 86% at 3.4 g COD/litre/day to 76% at 12.1 g COD/litre/day. High rates of treatment efficiency (TE) were recorded at low OLRs (<6.8 g COD/litre day) with a notable pH of the effluent increasing from 4 to neutral values. TS reduction was achieved at 57% at HRT of 2 d. This study indicated that biological methods can be used for treatment of potato-processing wastewater in order to reduce the organic load and other pollutants acceptable levels for municipal discharge.
This survey aimed at identifying the current practices and experiences of industrial wastewater treatment in Zimbabwe. In this study, questionnaires were used to assess various companies located in Gweru Kwekwe, Bulawayo and Harare. The information collected identified a gap in the treatment of wastewater from food processing industries in Zimbabwe. Current results indicate that about 86% of the food processing industries surveyed have primary treatment facilities. Few companies have proper secondary treatment facilities. Wastewater was characterised for selected effluents. Electrical conductivity (EC) of the wastewater was also recorded to be lower in most of the samples where dairy effluent showed highest EC by a value of 953 μS/cm. Total dissolved solids (TDS) were observed to be higher in dairy effluent as compared with other effluents. Total suspended solids (TSS) of cereal beverage effluent were higher with a value of 90 mg/L. The highest chemical oxygen demand (COD) values were recorded in potato processing effluent (690 mg/L O 2 ) followed by meat processing effluent (485 mg/L O 2 ). These values however are above the value recommended in Statutory Instrument (SI) (S.I.) 6 (S.I.6) of 2007 of 60 mg/L. It was noted that more than 80% of the wastewater comes from production processes and a substantial amount (53%) coming from raw material processing. This study indicates that regular inspections are done to enforce the wastewater legislation. Of all the companies studied, 73% of the companies were disposing their industrial effluent directly into the municipal sewer lines. Without the proper treatment facilities, the disposal of polluted effluent into the public sewer poses health and environmental consequences to the community. It can be concluded from the current data that there is a serious need to establish secondary treatment systems to remove organic load from food processing effluent and reduce pollution.
Wastewater from a mahewu processing plant was collected for characterisation and jar testing using Ferrifloc 1820 and a combination of Ferrifloc 1820 and the polyelectrolyte Magnafloc. Treatment showed that Ferrifloc 1820 caused a statistically significant decrease on both the chemical oxygen demand (COD) and oil and grease content of the wastewater. The mean decrease for the COD using Ferrifloc 1820 was 65.24% with the mean oil and grease reduction using Ferrifloc 1820 being 94.58 %. The polyelectrolyte Magnafloc was shown to have a statistically significant impact when used in combination with Ferrifloc 1820 on the COD. However, it did not show any statistically significant impact in the reduction of the oil and grease content of the wastewater. Although the treatment of the wastewater using Ferrifloc 1820 yielded significant results in the reduction of COD and oil and grease, the resultant results did not meet the Zimbabwean legislative standard for discharge. The resultant decrease of the oil and grease of the mahewu effluent due to this treatment makes it desirable to apply the use of Ferrifloc 1820 as a pre-treatment method for anaerobic digesters. There is need however, to determine the optimal pH and temperature and other operational parameters for Ferrifloc 1820 in the treatment of the mahewu wastewaters.
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