Mar 30, 2012
Anaerobic digestion in wastewater treatmentBack
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Water and wastewater management company Talbot & Talbot continue to successfully build and operate Upflow Anaerobic Sludge Blanket (UASB) digester treatment systems for companies throughout South Africa and Africa, across a range of industrial sectors.
“It is widely accepted that while anaerobic digestion is a proven, effective and highly efficient treatment system, upsets in performance remain common. A correctly run digester will efficiently convert up to 95% of organic material into a low-odour stabilised slurry and produce a renewable resource in the form of biogas that can be flared or used on site.
“This eliminates the need for additional solid handling and large-scale pond systems and limits reliance on nonrenewable fuels. Digester disturbances, however, continue to represent a significant risk limiting the widespread adoption of this technology,” the company highlights.
Under the Department of Water Affairs’ (DWA’s) water use licence conditions, the discharge of untreated effluent into water bodies, following reactor failure, can attract noncompliance penalties of millions of rands and, under special limit conditions, the forceful shutdown of operations for lengthy reseed periods of the digester.
Consequently, new applications are often over-engineered, under-loaded and relatively expensive.
“Despite decades of research into anaerobic digestion technology, a fundamental understanding of upstream effluent management, system sensitivity and basic process control continue to be highlighted as ongoing concerns, severely limiting the reputation and diversification of this technology,” notes Talbot & Talbot.
Digesters vary in capacity from 1 Ml/d to 5 Ml/d, treating between 1 t and 25 t of chemical oxygen demand a day, under general limit and special limit licence conditions.
The company believes that a high-performance anaerobic digester (AD) treatment system is attributed to a fully integrated approach, which begins with a systematic site water management plan and process optimisation within a client’s core business.
“Upstream focus is essential in preventing discrepancies in effluent data, which results in incorrectly designed, overloaded and poorly performing digesters; in segregating and correctly disposing of solid waste streams; and in ensuring potentially harmful contaminants are identified and isolated from the effluent system,” it states.
Plant design and construction is offered on a full turnkey basis, in addition to a full aftercare service through Talbot Operations, a business division of Talbot & Talbot.
This includes operator training, performance review and compliance monitoring on a support basis, as well as a dedicated team of competent operations and maintenance personnel on a fully outsourced basis.
“In addition, effluent sampling schedules are implemented through Talbot Laboratories to rapidly identify changes in effluent quality and monitor final discharge compliance. This guarantees the long-term treatment potential of UASB technology and a full commitment to the industry, which cannot be achieved on a build-only basis,” the company says.
A well-managed, high-performance AD system provides clients with the opportunity to recover water and energy resources from their effluent.
Secondary treatment systems in the form of activated sludge, sequential batch reactor and biofilter technology provide good-quality effluent treatment options, while water reclamation can be incorporated by ultrafiltration and reverse osmosis technology.
More recently, Talbot & Talbot have successfully designed and commissioned biogas recovery systems that capture the by-product of digestion, methane, as a renewable, carbon dioxide-energy source.
A 25 t digester with a biogas production of 6 500 Nm³/d can typically produce 52 t/d of steam, which supplements nonrenewable energy use by up to 15%.
“The realised value of a biogas recovery project (BRP) can be directly comparable to the cost of the fuel it replaces, the logistical cost of supplying fuel to remote locations and the availability of electricity throughout Africa.
Despite these benefits, Talbot & Talbot state that the real value of BRPs is the renewed interest in AD technology, a deeper understanding of good effluent handling practises and an ongoing commitment to ensuring anaerobic digesters reach their full treatment potential.
Edited by: Chanel de Bruyn
Creamer Media Senior Deputy Editor Online
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