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Case Study: Turning agribusiness wastewater clean and harvesting green energy

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article image Biogas is used to heat boilers

CST Wastewater Solutions presents a cost-effective technology from Global Water Engineering (GWE) that simultaneously increases the quality of wastewater produced by agribusiness while disposing of an expanding odour pollution issue.

Deployed to assist crop and livestock operations achieve higher environmental standards, GWE’s COHRAL technology involves a covered high rate anaerobic lagoon that uses concentrated anaerobic bacteria to digest 70 per cent of the organic matter (COD, or Chemical Oxygen Demand) in wastewater to produce effluent of far higher quality than open lagoons.

Even higher water quality standards exceeding 90 per cent COD removal and up to 99 per cent in some instances, can be achieved by using GWE anaerobic and complementary technologies contained in totally enclosed tanks, or reactors, making it suitable for discharge in surface waters, says CST Wastewater Solutions Managing Director, Mr Michael Bambridge, whose company represents GWE anaerobic wastewater technologies in Australasia. 

GWE’s COHRAL technology eliminates many of the odours associated with open lagoons often used in meat, dairy and crop waste processing, which are increasingly leading to environmental protests and land use conflict as urban expansion and rural businesses operate in greater proximity to each other, says Michael Bambridge.

Another major benefit of covered anaerobic lagoons and totally enclosed anaerobic reactor systems is that the methane biogas produced within them by the anaerobic process can be collected and used to feed steam boilers and processing plants, replacing fossil fuel. This has been demonstrated in many GWE applications worldwide to repay for the cost of an anaerobic system in as little as a year or two, and then to go on to save thousands and millions of dollars in fossil fuel costs over succeeding decades. 

The first COHRAL installation in Australia to be employed at a meat processing and packing plant will feature reuse of the biogas in the boiler.

Michael Bambridge explains that open lagoon wastewater treatment systems were popular with industry because they were simple, cheap and easy to operate, allowing an ‘end of pipe’ solution to wastewater issues. However, governments all over the world are acknowledging the environmental downsides of the open lagoon systems, including their poor ability to control algae and suspended solids in warm weather and poor efficiency in removing pollution load.

COHRAL covered lagoons

COHRAL (COvered High Rate Anaerobic Lagoon) installations represent a major advance over open lagoons and are suitable for solutions involving less technology-intensive applications that allow a long process residence time and where adequate space is available. They are a cost-efficient first step toward totally enclosed reactor type anaerobic technologies.

COHRAL anaerobic lagoons consist of two zones, with the complete surface of the lagoon being covered by an influent distribution system. 

While the first and largest zone receives the major part of the incoming wastewater and is where the anaerobic digestion occurs, the second, smaller part of the lagoon serves as a post-digestion and pre-settling zone where a partial clarification of the effluent wastewater takes place. Settled sludge collected in this zone is pumped back to the inlet of the lagoon.

Only part of the anaerobic effluent is recycled back to the lagoon while the remaining effluent of the lagoon flows by gravity towards complementary technology such as the GWE proprietary SuperSep-CFS separation technology being used in the first Australian installation. 

Simplicity and energy efficiency are the major benefits of the COHRAL system with no additional mixing facilities required in the anaerobic lagoon. The influent distribution system acts as a hydraulic mixing system, converting a standard low load/low efficiency lagoon into a COHRAL system with increased efficiency.

The COHRAL system is also designed for safety with each anaerobic lagoon covered by a special floating membrane to retain the methane produced. A typical feature of GWE’s COHRAL system is the operation at zero biogas pressure (-1 to +1 mbar range). A sensitive membrane level measurement system controls the speed of a biogas extraction fan bringing the gas at 20 mbar to go to the flare. Compared to ‘inflated’ single membrane covers, the risk of leakage is virtually nullified.

Simplicity also extends to the Scada computer control system typically employed with COHRAL technology. All indications and alarms, as well as reporting on the daily operation of the plant, and trending can be done by a Scada computer system, which can also control all motor start/stop as well as auto/manual functions.

Applications of anaerobic technologies

GWE’s technologies serve a wide range of industries typically with high-strength effluents, with more than 5 million kg COD/day being treated by GWE installations worldwide. These cost-efficient and user-friendly technologies – as proven in more than 300 industry plants worldwide in 60 countries – were most recently used in Australia to reduce the dependence of the $120 million Bluetongue brewery on fossil fuels and ultimately cut its overall energy needs by 15 per cent.

GWE’s anaerobic technologies are serving clients in agro and agro-processing, animal manure, beer and beverages, food processing and canning, and snacks, confectionary and dairy industries.

Anaerobic wastewater treatment

GWE’s seven proprietary anaerobic reactor types offer a truly unique range, each specifically designed for dedicated organic loads.

GWE’s main anaerobic reactor family, the ANUBIX-series is based on the Up-flow Anaerobic Sludge Blanket (UASB) technology and is available in three different designs: 

ANUBIX-B is designed for low-to-medium strength wastewaters with moderate TSS and no FOG (fat, oil and grease).

ANUBIX-C is designed for medium-to-high strength wastewaters with higher TSS and some FOG.

ANUBIX-T is designed as a tower-shaped EGSB (Expanded Granular Sludge Bed) for low-to-medium strength wastewater with low TSS, and strict space limitations.

When UASB solutions are not sufficient such as for salty wastewaters, and water containing lots of fat, oil and grease (FOG) or nasty chemicals that induce flotation in the UASB reactor, GWE offers several additional anaerobic reactor types, providing dedicated solutions for specific problems:

FLOTAMET or FLOTAtion METhane reactor, which has additional mechanical mixing incorporated and a separate Dissolved Biogas Flotation (DBF) module, and is highly suitable for treating FOG-rich and salty wastewater as well as wastewater containing a lot of proteins or fibres; 

ANAFIX or ANArobic FIlter reactor, containing a plastic biomass carrier material throughout the reactor to create an optimal environment for treating wastewaters from the chemical industry with a low amount of suspended solids; 

ANAMIX or ANAerobic MIXed digester, a proprietary reactor type with good mechanical mixing that allows better treatment of concentrated wastewater as well as sludge and slurries with high FOG concentrations’

COHRAL or COvered High Rate Anaerobic Lagoon, uses high quality UV-resistant materials, and is a less process-efficient installation in terms of loading rate, but can sometimes offer a solution for less technology-demanding applications that allow a long residence time and where plenty of space is available.

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