Technical Yearbook 2024

MAY

Biosand reactors as a feasible solution for the treatment of winery wastewater (Part 1) By Gareth Holtman, Rainer Haldenwang & Pamela Welz

remediation of WWW. Lessons learned from these studies have led to the development of a prototype. Results of the most recent studies and their practical applications are briefly presented in this report. Set-up and operation of pilot biosand reactors Biosand reactor systems consist of infrastructure for primary settling, WWW equalisation, and biological and physicochemical treatment. The latter two functions occur in one or more BSR modules, as shown schematically in Figure 1. Modules can be added to the system to scale up treatment capacity. Good flow rates can be achieved when applying the WWW to the top of the sand and allowing it to percolate through the sand, in other words, when the BSR modules are operated vertically. In the sand matrix, (1) bioremediation (removal) of the organics takes place, and (2) acidic WWW is neutralised without having to add chemicals. A unique design feature is the adjustable outlet, which controls the flow rates by increasing or decreasing the hydraulic head within the BSR modules. The higher the hydraulic head, the higher the water pressure in the sand and the higher the flow rate. An example of how this is applied is during the crushing season when WWW treatment systems need to deal with high organic loads. More organics equate to more substrate (food) for the microbial populations. The microbial biofilm, therefore, proliferates and reduces the pore spaces in the sand, decreasing the flow rate. This can be counteracted by increasing the water pressure by temporarily manipulating the height of the outlet until the organic load and biomass decrease after the crush period. In wineries where sufficient solids are removed from the existing primary settling infrastructure, the WWW can be directly applied to the BSR surface. If the WWW has high concentrations of solid particles, secondary settling may be necessary. The set-up of a pilot system requiring infrastructure for additional settling is depicted in Figure 2. Apart from the solids settling function, using additional settling tanks has an advantageous buffering effect because it reduces the variability of the influent to the BSRs.

Introduction Winery wastewater (WWW) is classified and regulated by the Department of Water and Sanitation (DWS) as “biodegradable industrial wastewater”. In many wineries in South Africa, WWW is used for irrigation after the solids have been reduced in settling deltas or oxidation ditches and the pH has been adjusted. Depending on the effluent’s quality and quantity, this can negatively impact the receiving environment over time. Passive treatment systems such as constructed wetlands (CWs) have been used to remediate WWW. However, plants can die when exposed to high concentrations of polyphenolics, which are often present in WWW. Constructed wetlands typically contain gravel, sand, or both as the media for the attachment of the functional microbial biofilm and plant growth. Biosand reactors (BSR) are essentially unplanted CWs that are easier to maintain than their planted counterparts. A number of laboratory-based and pilot studies have been conducted to determine the effectiveness of BSRs for the Abstract Based on over 10 years of laboratory and pilot scale studies, a prototype biosand reactor system for remediation of winery wastewater is proposed. In these systems, organics are bio-degraded by microbial communities and acidic winery wastewater is neutralised via calcite dissolution into calcium and carbonate. The calcium released into the effluent also decreases the sodium adsorption ratio, protecting the receiving environment from sodicity. By using locally available sand with particles ≤0.425 mm removed, systems can be designed to adjust the flow rates to achieve the desired hydraulic retention time for optimal remediation of winery wastewater. This article reports a basic synopsis of the practical findings of the research. In-depth scientific results are available either online or by request from the corresponding author.

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TECHNICAL YEARBOOK 2024