The effect of hydraulic conditions on the performance of an upflow anaerobic filter at ambient temperatures treating synthetic winery wastewater
Date
2024-03
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Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Wineries produce wastewater throughout the year, although peak production is experienced during harvest and bottling periods. Winery wastewater (WWW) also varies in strength and composition throughout the year, with COD concentrations ranging from 400 mg/ℓ to 50 000 mg/ℓ. Major components of the COD in WWW include monosaccharides, ethanol, and acetic acid. Wineries seeking to mitigate their demand for fresh irrigation water while adhering to legal wastewater treatment standards are presented with various treatment options. Among these, anaerobic wastewater treatment provides an environmentally friendly and effective option. However, anaerobic wastewater treatment systems can be expensive to implement and operate. They are often complex to control, operate best at elevated temperatures, and can be extremely sensitive to environmental conditions and wastewater compositions, generally making them inaccessible to small-scale wineries. The upflow anaerobic filter (AF) is an implementation of high-rate anaerobic wastewater treatment that makes use of packing media within the digester to foster biofilm development. Upflow AFs are able to operate over a larger range of flow conditions to comparable upflow anaerobic sludge blankets (UASB) and require smaller digester volumes than suspended sludge continuously stirred tank reactor (CSTR) counterparts. Therefore, this research focused on the evaluation of an uncomplicated packed bed anaerobic system for the potential treatment of winery effluent, with only pH and upflow control while operating at ambient temperatures (set-point temperature of 22 °C). The experimental AF was a 3 m tall PVC column, with a diameter of 110 mm. It had a working volume of 25.7 ℓ and was packed with 25 mm plastic pall rings. A synthetic WWW (5 213 ± 376 mgCOD/ℓ) was used as typical feed to the AF. The pH of the solution entering the column was controlled at 7.2, while two hydraulic flow parameters were controlled, viz the hydraulic residence time (HRT) of fresh feed in the system and the upflow velocity through the column. These hydraulic parameters were manipulated by a fresh feed pump and a recirculation pump, respectively. The system pH, temperature, and biogas production rate were monitored through a bespoke Arduino data logging system. The biogas was produced at rates between 0.7 mℓ/min and 2.8 mℓ/min, with yields between 0.3 mℓ/mgCODconsumed and 1.1 mℓ/mgCODconsumed, and methane concentrations ranging between 46% and 72% (gas readings taken at ambient temperature and pressure). The system showed unstable and poor performance when operating at too low upflow velocities. Although, it consistently reduced the COD of the feed by more than 55% when operating at upflow velocities between 30 – 48 m/day and HRTs between 24 – 60 hours. The highest COD reduction of 69.5% was at an upflow velocity of 31 m/day and 42 hours HRT. In other words, when treating a synthetic winery effluent with ca 5 000 mg/ℓ COD, this simple system can comfortably reduce the COD levels to around 1 900 mg/ℓ. Since the system was able to operate acceptably at ambient temperatures over various hydrodynamic conditions (showing resilience to changes in selected operating parameters), it could perhaps be considered as a viable anaerobic treatment method for small-scale and boutique wineries. The Anaerobic Digestion Model No.1 (ADM1) was applied – with selected regressed parameters – to predict the COD reduction in a system of similar process design, but at different COD feed concentrations. https://scholar.sun.ac.za iii The final calibrated model was regressed against experimental data at and HRT of 42 hours and upflow velocity of 39 m/day. Assuming CSTR conditions, the calibrated model showed good effluent COD predictions (errors below 5.6%) of the optimal experimental conditions and offers a reasonable means of predicting the performance of the system.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MEng)--Stellenbosch University, 2024.