Proven wastewater technologies combine to double green energy and environmental benefits
Dissolved air flotation (DAF) is a tried and trusted treatment of industrial wastewater effluents produced by food, beverage and primary processing plants that are integral to the economies of many countries in Australasia, Asia, Africa, America and Europe.
DAF’s great strengths as a primary treatment include its relative simplicity in installation and proven cost-efficiency in separating oil and suspended solids from wastewater in applications as diverse as dairy, beef, pork poultry, grains and cereals, and crops such as beets, cassava, potatoes, soy, wheat, corn and sugar cane.
Compact and robust DAF systems reduce chemical oxygen demand (COD) loading by the removal of high COD contaminants including fats, oils and greases, colour, organic matter and colloidal material. A reduction of up to 70-80% COD and suspended solids can be achieved in some instances with chemical addition.
But impressive as these results are, they may not always be enough. As environmental and cost-efficiency demands increase on food, beverage and primary processing plants - and as such plants increasingly overlap with expanding urban areas - they face the twin pressures of achieving ever-higher wastewater discharge and waste disposal standards while also achieving greater cost-efficiencies.
Neighbouring communities these days won’t tolerate groundwater pollution and air pollution in the form of smells from piles of rotting sludge and by-products. Shareholders, meanwhile, demand that any solution be ecologically sustainable and highly cost-efficient.
These twin demands used to present a virtually indissoluble dilemma, a real paradox, because better environmental technologies cost more, not less. But not any more. Because proven DAF technologies can be very profitably combined with the latest anaerobic waste digestion technologies which not only extract very high levels (up to 90%) of harmful COD contaminants from wastewater streams and sludge by-products, but also convert them into profitable green energy.
The sludge floated in the DAF process can be anaerobically digested, thus eliminating a sludge dewatering and sludge disposal issue. Anaerobically digested sludge produces methane, which can be used to fuel boilers.
This biogas (methane) can be used to fuel boilers and heat processes, replacing costly and polluting fossil fuels. Or, if there is enough biogas, then it can be fed to generators for conversion to electricity that can be fed back to local grids and used to achieve carbon credits or pollution reduction credits. The United Nations has backed this method of achieving localised and highly efficient sources of electricity, which don’t suffer from the same energy losses as centralised electricity systems and do benefit their local communities.
“DAF and anaerobic digestion are very complementary technologies, which offer double benefits in the form of far cleaner effluent and green energy (methane biogas) to cut fossil fuel bills and pollution,” said Michael Bambridge, an authority on both technologies. Bambridge is managing director of CST Wastewater Technologies, which has installed DAF systems for numerous primary producers and food processors in Australasia over the last 20 years as well as advanced anaerobic digestion systems.
Examples of anaerobic benefits
Livestock
One of the most recent projects undertaken by CST Wastewater solutions is the GWE COHRAL (Covered High Rate Anaerobic Lagoon) at Oakey Beef Exports on Queensland’s Darling Downs, which will extract green energy biogas from its wastewater streams to replace millions of dollars’ worth of natural gas currently consumed by the abattoir.
The plant is expected to repay its cost of construction inside five years through gas purchase savings amounting to many millions of dollars - then continue to deliver benefits and profitability virtually in perpetuity, says Oakey Beef Exports Pty Ltd General Manager Pat Gleeson. Adoption of the technology is the result of an exhaustive selection process and the committed alliance to the environment of Oakey Beef Exports and its owners Nippon Meat Packers, Gleeson says.
Dairy and potato
Another outstanding example of the efficiencies of anaerobic technologies is provided by Remo-Frit, in Belgium, which has demonstrated the environmental and economic benefits of converting waste products into green energy, transforming a potential problem into a sustainable solution offering greater profitability.
Out of a 3300 m3 digester for the potato peels and primary sludge, GWE is able to produce up to 14,150 m3 of biogas per day from ±230 ton of organic residues per day (potato peels + primary sludge).
On top of that, the anaerobic wastewater treatment plant produces another 3350 m3 of biogas per day. Together, this amount of biogas is equivalent to 8410 kg or 9834 L of light fuel oil per day or 3106 tons of fossil fuel a year, worth nearly €3 million or nearly US$4 million.
Energy savings produced by biogas production at Remo-Frit are achieved in perpetuity, with fossil fuel equivalent savings totalling US$40 million (nearly €30 million) in the first decade at today’s prices.
Dairy
One of the United States’ newest dairy processing plants features advanced anaerobic wastewater treatment technology that not only radically improves biomass recovery and effluent quality, but also harnesses green energy from waste streams to drive production processes and reduce its carbon footprint.
The Cayuga Milk Ingredients (CMI) plant in Auburn, NY - which is scheduled to commence production this northern summer - will manufacture a wide range of dairy products, such as pasteurised cream, whole milk powder, liquid permeate, condensed milk, skim milk powder, non-fat dry milk and milk proteins.
Cayuga Marketing LLC - a collective of dairy farmers in the Finger Lakes Region, NY - decided to construct their local processing plant to reduce their milk-hauling costs while also greatly reducing transport emissions and carbon footprint as a result of the shorter transportation distances involved.
To achieve optimum environmental and efficiency benefits, CMI further decided to implement an anaerobic treatment process for their wastewater treatment facility, seeking to simultaneously achieve the most environmentally effective, energy-efficient and cost-efficient solution.
Starch
Similar success extracting biogas from both wastewater and waste pulp has been achieved at the Chok Chai cassava plant in Thailand, a finalist in the energy category of the prestigious 2014 IChemE global awards run by the Institution of Chemical Engineers representing 40,000 members across 120 countries.
Chok Chai uses GWE’s RAPTOR anaerobic wastewater technology with ANAMIX thermophilic digester for the processing of waste cassava pulp and its conversion into biogas.
Chok Chai Starch’s Thermophilic RAPTOR - the world’s first plant to incorporate the thermophilic biological digestion process for cassava pulp - not only greatly reduces leftover pulp, but boosts the plant’s existing biogas production to replace fossil fuels and to generate electricity.
The latest technology installed at Chok Chai Starch helps the factory achieve a minimum of 80% conversion of the organics present in the pulp to biogas (methane), treating a maximum of 370 tons a day of wet pulp containing 68,700 kg a day COD (chemical oxygen demand). Daily biogas production exceeds 30,000 Nm3 at 60% CH4 content.
Conclusion
Community and government demands for clean water and renewable energy are expanding globally, while tolerance for ground and air pollution is disappearing fast.
However, few technologies are available that simultaneously offer efficient primary and secondary processing of compounds commonly encountered in the food and beverage industry (see Table 1), while also providing green energy to offset and ultimately eliminate the cost.
| Compounds | Sources | Examples |
|---|---|---|
| Carbohydrates, sugars, starch, cellulose | Beets, corn, potatoes, maize, straw, grass | Sugar beet and starch processing waste, manure, harvest remains |
| Proteins | Animals and animal products | Milk and dairy processing waste |
| Fats | Animals and animal products | Slaughterhouses, rendering plants |
| Volatile fatty acids | Fats, oils, grease, evaporation condensate | Slaughterhouses, rendering plants, oil mills |
In all of these areas, DAF primary treatment technologies and anaerobic secondary technologies offer widely proven means by which to cost-efficiently achieve environmental objectives and boost profitability.
However, it is often no longer simply a choice of one or the other: the best results will be had from a combination of both, engineered to the needs of particular industries.
Combined DAF and anaerobic plants - including breweries, fruit, food waste, agro industries and energy crops including corn - employ proven technologies to open the door to major environmental and production efficiency gains globally.
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