Over 80% of the world’s wastewater is simply discharged to the environment untreated, according to the UN. This not only damages ecosystems, natural water quality and human health but wastes a potentially valuable resource.
Many industries need large volumes of water in their product make-up or for related activities such as wash-down equipment. Despite increasingly efficient cleaning-in-place (CIP) and sterilisation-in-place (SIP) systems, water consumption remains high and much of it drains wastefully away. That wasted water could instead be collected and recycled, with appropriate purification, for reuse in the same industrial processes or for a variety of alternative purposes.
Recycling immediately reduces the amount of raw water you need to buy, and it may also cut costs relating to wastewater disposal. Regulators or municipal authorities often charge industrial customers according to the volume and condition of their discharges. If limits on quantity and quality are exceeded, there may be excess fees or fines to pay.
Before discharging, you may already be having to pay someone to treat your waste stream. In cases where the wastewater is being pumped to another site for treatment, equipment and energy costs can be lowered by recycling it close to its point of use. If the quality of the recycled water is insufficient for your operations, someone nearby might buy and use it for theirs.
These savings must be weighed against the set-up and running costs of water recycling facilities, with consideration of how long you can afford to wait for a return on your investment. For many businesses, the ROI has turned out to be surprisingly fast.
As water prices and discharge fees rise, and regulations on discharged water quality become more stringent, the business case for recycling is strengthening. At the
same time, growing public concern over environmental issues is putting extra pressure on businesses to act responsibly. In assessing the economic viability of reusing your wastewater you should factor in the PR value of maintaining a reputation for sustainable practices and social responsibility.
A key question is how clean the water needs to be after treatment. There is no commercial value in improving water purity beyond the demands of the process needs. For example, if recycled water is to be used for irrigation of agricultural or amenity areas, toxins must be low but suspended inorganic solids are unlikely to be a problem. Similarly, water reused for flushing toilets and other sanitary systems need not be of drinking quality.
Purification costs will depend on these considerations and on the content of the wastewater. The most costly and specialised purification techniques are often used to remove contaminants which are harmful even in small amounts.
Key purification options include:
Clarification - Organic and inorganic particles suspended in cloudy water are clumped using coagulant chemicals, then separated out by sedimentation or filtration.
Dissolved air flotation - Air dissolved into water under pressure is released as small bubbles. Suspended oils and solids stick to these, float to the surface and are removed by skimming.
Digestion - Organic material is broken down into simpler constituents by micro-organisms. Anaerobic digestion (AD) (without oxygen) can generate methane as a useful by-product. It may be followed by AD to reduce organic content further.
Distillation - This separates water from substances with higher boiling points.
Filtration - Mechanical filters may remove large items such as grit, dirt and fibres. Finer filtration systems capture particles larger than a micron.
Microfiltration and ultrafiltration -Membrane filters remove very small particles and, if necessary, prepare water for reverse osmosis and/or deionisation.
Reverse osmosis - Water is forced through a semi-permeable membrane which traps very small particles and larger molecules.
Deionisation - Ion-exchange resins replace unwanted ions like calcium and magnesium with relatively harmless ones like sodium. Electro-deionisation increases effectiveness by electrically regenerating resins. Adding softeners such as calcium hydroxide, can remove targeted solutes by precipitation.
Disinfection - Micro-organisms can be killed by UV radiation, ozone filters or traditional chlorination.
To be sure of the most efficient and cost-effective combination of wastewater treatments, you should consult a water purification specialist, such as SUEZ Water Purification Systems. Having established the initial and ongoing costs, it should be easy to decide whether recycling is economically viable for your operation.