Key points
Solid organic waste and wastewater is an increasing issue for food processing, water treatment and some pharmaceutical sectors. Craig Shaw, CEO of Advetec, a leading UK specialist in advanced environmental technologies for the treatment of effluent and solid waste, explains why extremophile bacteria and biothermic digester technology could be the solution
Solid and liquid biological waste
Food processing industries including brewing and beverages, dairy, ready meals, meat processing and abattoirs, as well as the pharmaceutical and waste water treatment sectors all need to deal with solid and liquid biological production residues that are rich in nutrients and organic content. Until recently such production residues have been regarded as a costly overhead which requires treatment before safe discharge to sewers or disposal off site.
Issues faced by food processing industries
Food processing organisations must address various issues in order to meet environmental targets. Disposal of waste by-products is a heavily-regulated area which is becoming increasingly stringent. Food manufacturers must meet Trade Effluent Consents and require pollution prevention and control (PPC) permits or Waste Management Licences.
Reducing Biological Oxygen Demand (BOD) to meet trade discharge consents is also a major issue. There is growing pressure from the UK government to reduce the biological load in wastewater discharged from production processes and for zero organic waste to be sent to landfill.
We see similar environmental pressures in the USA and Europe. Legislation and taxation are pushing hard to limit dumping, but in many instances there are few alternatives. And all the while volumes are increasing…
A high water content makes solid and liquid waste very expensive to transport, as well as costly and inefficient to incinerate. As a result, most production facilities require an on-site effluent treatment plant.
Current treatments
Conventional processes to treat biological waste include settlement tanks, sand filters, membrane filters and bioreactors, activated sludge processes and dissolved air flotation (DAF) systems, plus expensive chemical interventions – all designed to filter out and remove suspended solids, BOD, plus oils and greases – to leave clean water. The focus here is on reducing the biological load so that waste water meets discharge consents.
However, the problem still exists of dealing with the solid residues which need to be hauled away for disposal to incineration or landfill. In addition, they are not particularly suited to dealing with solid food waste or waste containing a mixture of different solids.
Anaerobic Digestion (AD), which is becoming increasingly popular, can provide part of the solution, but even here a considerable residue is left as the AD process is unable to deal with some of harder-to-digest organics. Throughput is also slow and incorrect loading of waste material, combined with the inability to control the internal environment, or the digestive rate of the bacteria, frequently leads to poor performance and breakdown of the process.
This requires the machine to be manually emptied and then eventually restarted. This process does not guarantee a certifiable product either. To compound the problem AD infrastructures can take up significant space and the process tends to be slow.
Latest bio-thermic digester and bioreactor technology
One approach is to use advanced thermal technologies and extremophile bacteria to literally consume all of the organic material – or certainly a much higher percentage than conventional solutions – leaving a small inert residue for use as RDF (refuse derived fuel) or as a soil improver, and clean water.
In California for example, where environmental regulations for waste organics are increasingly stringent and both disposal and haulage costs are prohibitive, a recent trial for pre- and post-consumer food waste for example achieved a better than 91% reduction rate.
Bio-Thermic Digester (BTD) technology is an in-vessel solution engineered to rapidly digest organic waste. As well as being optimised for fast throughput it also has a smaller footprint than other processes, an important factor where site space is limited.
More importantly it is able to handle a wide spectrum of organic material including normally indigestible hard carbons, cellulose and lignin-based materials. In addition to food waste therefore, it can also handle organics from abattoirs, sewage sludge, as well as waste from fat traps, septic tanks, filter cakes, gully cleaning and trade effluent, and of course green waste.
At the heart of the process is a blend of extremophile bacteria and specially-developed nutrients on which the bacteria thrive at high temperatures, enabling them to rapidly digest all of the organic material. This innovative thermal process has proved to be far more efficient than AD alone.
The latest bio-thermic digesters have been designed to minimise the need for further processing whilst enabling food processing companies and the like to discharge clean water to sewers within Integrated Pollution Prevention and Control (IPPC) regulations.
The advantages of such a high temperature aerobic digestion process, is that it is extremely rapid by comparison to conventional in-vessel composting. Some equipment has a heat and moisture recovery system which improves biological efficiency and reduces running costs.
This takes heat generated by the exothermic process and re-uses it to sustain the high temperature environment (90-125 Dec C) required for the bacteria. This can cut energy running costs by as much as 60%.
Biothermic digesters are also impervious to contamination and some can digest all the organic matter present in mixed waste in just 72 hours. Consequently, operating costs drop after the initial start-up procedures.
Water from steam is condensed out and filtered to deliver a similar quality to tap water if required and all moisture extraction and odour control are built into the system as standard.
Bio-Thermic Digesters will safely convert 32+ tonnes of organic food waste into water and a dry powdery by-product. The on-site process can deal class 3 type animal by products wastes such as feather, blood and offal from every stage of dairy, slaughterhouse and food production process, which only takes around 72 hours.
This new technology has been trialled in various applications over a period of four years in the UK, the US and the Middle East and now there are pilots starting in Italy and Spain. Key to the process is an in-depth understanding of aerobic bacteria, along with the nutrients and bio-stimulant technology used to invigorate and speed up the digestion process.
Of course not all waste streams are the same and continuing research blending different strains of extremophile bacteria and the nutrients that encourages them to thrive, is helping to answer the problem of dealing with more complex organic waste streams.
Operating environments are different too and careful monitoring and adjustments of the internal process including temperature, nutrients, oxygen and waste gases, is key to optimising throughput and maintaining the health and activity of the bacteria.
Developments here in terms of remote telemetry and the control software enables the delivery of completely managed services for customers, operating a machine 24/7 anywhere in the world from UK facilities.
A BTD needs to be part of a complete advanced engineering system consisting of hoppers, shredders, augers, storage tanks and piping, designed and tailored to match each customer’s differing needs to increase throughput and ensure an optimal and robust processing environment.
With the growing requirement to limit or end the disposal of organic waste to landfill and ever stringent environmental consents for the discharge of wastewater to sewers, the ability to fully process waste water and solid waste from production processes on site, effectively plumbed in to the manufacturing process, is becoming increasingly important.
Conventional systems only provide part of the solution. Extremophile bacteria and bio-thermic digesters can help complete the waste management cycle. For smaller sites with limited space they might offer the only solution.
