Lay waste to poor treatment03 December 2014
There are many ways to clean up performance of water and effluent treatment units in industrial plants. Steed Webzell takes a look at some of them
Although a wide range of plant equipment, instrumentation and controls is meat and drink in water treatment – which is necessarily geared towards automation – ageing plant, tighter regulations and rising energy costs are forcing the emergence of new ideas for process water and effluent treatment.
Put simply, inadequate effluent treatment can land companies in trouble with the authorities. This is a worry as industrial effluent is a by-product of many processes, whether it's in the metals industry (anodising, phosphating), paper and packaging, textiles (dye and PVA recovery), pharmaceuticals or, of course, the food and beverage sector.
Where liquid waste from factories contains waste such as food, bio-digestion represents an effective disposal route. Significantly, rather than the vast anaerobic digection plants that have been springing up around the country, said technology is now available on a scale suitable for implementation at factories and manufacturing sites.
A case in point is Advetec's industry sized Bio-Thermic Digester (BTD), the first of which has been installed recently at Regional Waste Recycling (RWR) in Stratford, East London. Although not an industrial site per se, this technology would sit equally comfortably at a food or beverage plant, for example.
The BTD can reduce liquid and organic waste from fat traps and filter cakes, for instance, by 97% to just water and dry sterile powder. The water is clean enough to be used for purposes such as irrigation or washing.
The machine at RWR is processing up to 33 tonnes of organic waste every 72 hours. Instead of typical landfill costs of £80–£90 per tonne, the company's costs are now around £1.99 per tonne to process on site, offering ROI within 18 months.
Unique here is Advetec's understanding of aerobic bacteria, the bio-stimulant technology used to invigorate and accelerate the digestion process: the control and motivation of the thermophilic bacteria within the unit, and the replenishment of essential micronutrients, ensure they remain healthy.
In fact, the use of thermophilic bacteria (which thrive in heat) allows the BTD to run at temperatures in excess of 180°C, far above other in-vessel solutions. This not only accelerates the process, but makes it possible to digest already part-treated material from AD plants, for example.
Of course, in many instances there are business opportunities beyond the simple disposal of waste. According to Esmil Process Systems, which specialises in the design and installation of process water treatment systems, the design of its solutions results in high degrees of water and product recovery as part of a membrane filtration stage.
The company insists that the recycling of water with concomitant product recovery now forms a key part of environmental performance requirements for many industries being assessed for best available technology (BAT) under European IPPC regulation.
The regulatory emphasis is on reduced water take, notably for high use sectors such as food and drink, and reduced waste disposal, either to sewer, discharge to the environment, or solids disposal by landfill or incineration.
For certain applications, membrane treatment using ultra-filtration – or even coarser micro-filtration – may suffice to allow adequate recovery of products and process water. In the food and pharmaceutical sectors, UF treatment systems typically utilise low pressure membrane cartridges (incorporating tubular, hollow fibre or spiral wound membrane technologies) to achieve this.
For other applications, separation of dissolved solids by nano-filtration or reverse osmosis is required, says Esmil. These systems typically operate at higher pressures than UF systems, but can result in excellent levels of product recovery and high percentages of water reuse. Treatment capacities range from 50 to 1,200m³ per day, although Esmil's modular systems can be linked to treat higher volumes if necessary.
For many plant engineers, ensuring that process water or effluent treatment systems are working efficiently demands the use of effective monitoring techniques. Parameters to keep an eye on can include pH levels, temperature, flow rate and suspended solids. Any fluctuations may offer early indication of potential problems.
Today, traditional and somewhat expensive meter chambers are being replaced with technology such as ABB's recently introduced MCERTS-approved WaterMaster electromagnetic flowmeters, which are purposely designed for process water and effluent flow measurement and management.
In line with the Environmental Permitting Regulations (EPR) legislation, all industrial companies discharging 50m³ or more of effluent per day to a watercourse or the sea should self-monitor their effluent flows.
Under this scheme, companies should be able to demonstrate, to the satisfaction of a qualified MCERTS inspector, that they are using BAT. EPR covers sectors such as chemicals and pharmaceuticals, food and beverage, power, pulp and paper, water and wastewater, and oil and gas.
ABB's WaterMaster is one of the first flowmeters to be awarded a Class 1 MCERTS conformity certificate for closed pipe flow measurement. According to Alan Hunt, ABB's product specialist for electromagnetic flowmeters, a major benefit to plant engineers of WaterMaster is its ability to deliver early fault indication.
A 'fingerprint' of parameters
So, how is this achieved? Well, after ABB builds each WaterMaster, key electrical parameters are checked, including the resistance of the magnetic-inducing coil and insulation of the coil to earth. These are recorded as a 'fingerprint' of parameters.
For instance, if the coil resistance measures 30 ohms, there is no fundamental reason why that measurement should change in service – unless there is a problem. Ta dah! Herein lies the ideology.
"The transmitter electronics runs a background task every 40 seconds to check the key electrical parameters and compare them with the fingerprint," says Hunt. "Any fluctuations might indicate that something is awry, such as a damaged cable, for example. Such a fault would be picked up before the process becomes unsustainable."
WaterMaster is also said to be the market's first "self-calibrating" electromagnetic flowmeter.
"The unit is given the ability to self-tune its operation within certain quality bandwidths," says Hunt. "For instance, a slight change in temperature is known to affect results in high gain electronics, but this would be compensated for automatically using WaterMaster. Of course, any significant discrepancies would lead to a suitable alarm being activated."
Technology is clearly moving fast. For those labouring with ageing effluent plant, the time is right to begin investigating ways that can prevent efficiency from wasting away.
Driving energy efficiency
Energy plays a key role in all water/effluent treatment applications. And yet, according to Phil Hall, industry manager at WEG, a huge amount of this energy is wasted as organisations use solutions that are poorly designed, inappropriate for their applications or are out of date. Hall suggests that by reducing this wastage, companies not only meet their environment responsibilities, but also cut their costs and improve their profitability.
The main culprits in energy consumption are the motors required to run equipment, such as pumps and blowers.
"It is important to note that the cost of a motor is not a one-off and doesn't end with the purchase: users will continue to pay for the motor long after the supplier's invoice has been paid," says Hall. "The purchase price of a motor is typically 1.8% compared with the running costs of 98.2%, which incorporate installation, maintenance, energy costs and downtime."
High efficiency motors that meet WIMES (Water Industry Mechanical and Electrical Specifications) and European Energy Using Products (EuP) standards can give significant cost savings if sized correctly and used in the right applications. Compared with a standard motor, a high efficiency model can be up to 3% more efficient, says Hall.
For example, a 90 kW high efficiency motor could cost £1,200 more to buy than the standard model, but will save £12,000 during a 10-year service life. The failure to fit a high efficiency motor may therefore cost the company £10,800 – a fairly hefty cost for what, at the time, may seem a small decision.
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