Turning Wastewater into Gold: ARC Researchers’ Biohydrogen Quest for Sustainable Agro-Processing
– By Zikhona Buyeye and Primrose Magama
ARC-Natural Resources and Engineering
South Africa’s agro-processing sector is a booming industry comprising largescale, well-established companies and a growing number of small-scale enterprises. It is a very diverse industry, spanning meat-, fish-, fruit-, vegetable-, grain-, sugar-, and milk processing as well as alcoholic and non-alcoholic beverage production. Agro-processing also includes tannery and the paper and pulp industries. As a result, wastewater produced by the sector is varied in nature, depending on factors such as the source, type, and level of processing activities. Regardless of its variation, the composition of agro-processing wastewater can make its treatment difficult and costly to manage. Insufficiently treated wastewater can negatively impact the environment, threatening the quality of human and animal life. Furthermore, conventional treatment methods do not harness the valuable resources contained in wastewater. Thus, resulting in a missed opportunity for wastewater valorisation. To seize this opportunity and contribute towards circularity in the agricultural space, the Renewable Energy unit under Natural Resources and Engineering at the Agricultural Research Council is currently undertaking research into the production of biohydrogen using dark fermentation. The research aims to demonstrate and evaluate the application of microbial biorefineries to produce biohydrogen and other value-added bio-products from agro-industrial wastewaters. The study looks to support the enhancement of sustainability and circularity in agro-processing by extracting valuable commodities in wastewater and producing cleaner effluent water that can potentially be reused before final disposal.
Agro-processing wastewater is (effluent) liquid waste that is generated when agricultural raw materials are processed into finished and semi-finished products. Depending on the processing activities, agro-processing wastewater typically contains a varying combination of high levels of organic matter, excessive nutrients, high concentrations of suspended and dissolved solids, bacteria, sugars, salts, fats and oils, detergents, and other constituents that complicate its handling and treatment. Proper treatment of agro-processing wastewater is essential to prevent environmental pollution and to ensure compliance with regulatory requirements. Typically, treatment of agro-processing wastewater is achieved in four stages, depending on the wastewater composition. These stages, namely preliminary, primary, secondary, and tertiary treatment, are done to improve final effluent quality. High-quality treated wastewater is, at times, re-used in processing facilities for landscape irrigation, toilet flushing, cleaning, and other non-potable uses. Wastewater re-use can reduce facilities’ freshwater intake, which is particularly valuable in South Africa considering the country’s water scarcity challenges.
Pre-liminary study results show that while most agro-processing companies apply secondary treatment, very few companies are extracting resources from their wastewater. Tertiary treatment is limited with sparce cases of on-site water reuse. A missed opportunity in resource recovery or on-site water reuse.
Conventional treatment practices perceive waste and wastewater as challenges to be addressed rather than opportunities to be exploited. However, changing environmental conditions and depleting natural resources are leading to a global paradigm shift in waste perception. Concepts like the circular economy model promote finding value in waste, thus minimising waste and maximising resource recovery while reducing reliance on raw materials. As such ARC researchers, in line with global trends, where there is a movement, although slow, towards resource recovery from waste and wastewater, are exploring waste valorisation for the local agro-industry. Ironically, the very characteristics that make agro-processing wastewater difficult to treat are what make it a promising resource for recovery. The high organic matter and nutrients contained in agro-processing wastewater can be extracted and processed into valuable commodities.
Nutrients, water, and energy are recovered from agro-processing wastewater through both proven and emerging technologies globally. Two most commonly recovered nutrients from agro-processing wastewater are nitrogen and phosphorus which can be extracted through various methods including chemical, biological and physical processes. Once recovered, these nutrients can be used as fertilisers. Water, in varying degrees of cleanness, can also be recovered from wastewater. Ideally, potable water should be recovered for reuse. However, water clean enough for other reuse purposes is sufficient. The goal of resource recovery is the overall reduction of reliance on raw resources. Energy generation from waste and wastewater is a fast-growing field. The recovery of energy from waste is pertinent considering that fossil fuel-derived energy is the primary driver of climate change. An added advantage of waste-derived energy over other types of renewable energy is the resultant reduction of waste through its generation.
A well-established process of energy recovery from waste is the anaerobic digestion of organic matter to produce biogas and a nutrient-rich digestate as a byproduct. Biogas digesters are growing in popularity because of their reduction in organic waste, feedstock diversity, and production of biomethane which can be used directly or upgraded to produce electricity. Furthermore, biogas digesters are suitable for varying locales due to their diverse nature; They vary from simple, household level brick-and-mortar digesters to complex, industrial scale digesters. Adoption of the technology is gaining traction in South Africa. The South African energy space stands to benefit greatly from waste-derived energy considering the country’s energy and waste handling woes.
Although it is still in its infancy, the production of hydrogen from waste – biohydrogen – can also play a critical role in the country’s efforts towards energy security, waste reduction, and transitioning to a green economy. Biohydrogen can be produced from various renewable sources such as food waste, agricultural waste, wastewater, and other types of biomass. Hydrogen has high energy content per unit of mass, and it burns clean and only produces water as a byproduct. This makes biohydrogen an even more attractive renewable energy source. Unfortunately, biohydrogen production is still limited to lab-scale research because of challenges associated with scaling up. Some of these limitations include process stability challenges, low yield, storage and transportation issues, and cost of production.
Nonetheless, continued research into addressing the aforementioned challenges and optimising biohydrogen production is vital to support the development of a green economy. Hence the ARC has undertaken research to help address some of the challenges. A crucial aspect of the research is participation of different stakeholders in the agro-processing sector, including industrial enterprises, treatment facilities, regulators, suppliers, academia, and environmental NGOs. In addition to wastewater information, stakeholder participation can provide perspective into the opportunities and challenges of implementing circular wastewater treatment in the agro-processing sector, ensuring that the research is insightful.
There is a major opportunity cost associated with the conventional perspective of waste management. Simply treating waste and wastewater for disposal fails to capitalise on the valuable resources that are contained therein. The agro-processing sector, in particular, stands to make a considerable contribution to resource recovery and waste management due to the nutrient and organic matter rich nature of the industry’s wastewater. Agro-processing effluent is not just a problem to solve; it is an opportunity to seize. With the right support, technologies like biogas and biohydrogen could transform South Africa’s waste into a vital part of its clean energy future. Turning this vision into reality will take more than innovative ideas, it will take action from industry, researchers, and policymakers.
Zikhona Buyeye is a junior researcher in the Renewable Energy unit at the Agricultural Engineering campus of the Agricultural Research Council. She is passionate about the advancement of renewable energy and sustainable agricultural practices. If you are a stakeholder in agro-processing or wastewater management, or an agro-processor interested in participating in the biohydrogen research study underway, please send an email to Buyeyez@arc.agric.za or Magamap@arc.agric.za for further information. Participation in the research is strictly confidential.
