All organisations have a responsibility when discharging wastewater into either sewerage system’s or watercourses to ensure it meets local and national requirements. A company’s trade effluent consent will require the composition of waste water adhering to specific criteria. These will vary but will normally include:
- Fat, oil and grease content;
- Suspended solids;
- Sulphates, heavy metals and other chemicals;
- Chemical oxygen demand;
- Biochemical oxygen demand;
- Flow recording.
Certain authorities will also specify how often water should be tested and systems audited.
Glenfarrow offer advice on all elements of waste water planning and will advise on local requirements and even offer a laboratory testing facility.
Waste Water Treatment Chemicals
There are four main types of chemicals used for wastewater treatment:
- pH neutralisers;
- Foaming agents;
Normally waste water being discharged into a sewerage system would have a pH range 6-10. pH is more important when waste water is being discharged directly into rivers, lakes or other water courses – this is important to ensure that natural wildlife and ecosystems are not harmed.
Coagulation is the process by which colloidal and finely divided suspended matter is caused to coalesce, leading to the formation of Flocs and agglomeration of the flocculated matter. This is often referred to as cracking out.
The coagulant would typically be aluminium or iron salts.
The volume of coagulant would be added either in a predetermined volume based on the ratio of waste water being delivered into the chemical contact chamber or to a predetermined pH band in the acid state.
The mechanical flash mixer in the chamber ensures that thorough mixing is achieved and the volume of the chamber ensures that sufficient dwell time is available for coagulation to be completed.
Before flocculation can be achieved, it is sometimes necessary to pH correct the coagulated waste water to a near neutral pH band.
Normally pH correction is carried out by the addition of sodium hydroxide (caustic soda). A predetermined pH band controls the volume of sodium hydroxide being added.
Again, the flash mechanical mixer in the chamber ensures that thorough mixing is achieved and the volume of the chamber ensures that sufficient dwell time is available for pH correction to be complete.
The pH corrected waste water is displaced into the third section of the chemical conditioning chamber where polymer is added on a volume-to-volume ratio and flocculation takes place. The typical polymer solution is 0.1%.
Flocculation is the coagulation and agglomeration of colloidal and finely divided suspended matter to form flocs.
Flocculation is achieved in the third section of the chemical contact chamber. The slow speed mechanical mixer ensures that adequate mixing is achieved and the volume of the chamber ensures that sufficient dwell time is available for the floc formation to be complete.
The slow speed mixer ensures that shearing of the floc does not occur.
The flocculated waste water is then displaced in to the final section of the chemical contact chamber which acts as a stilling zone and allows the floc strength to develop.
Many industrial and manufacturing processes rely on acidic or basic chemicals – from acidic etching of metal parts to the use of bleach to wash down food production installations – these are then flushed down the drain. pH adjustment (normally from acidic or basic) can be used in post process water treatment to precipitate out dissolved contaminants, such as heavy and toxic metals – these then need to be neutralised before discharge. The use of carefully controlled doses of compounds such as sodium hydroxide (NaOH) or strong acids during waste water processing is a simple way of ensuring the pH of the effluent discharged to the sewerage system is controlled.
Foam is caused by the formation of air bubbles in the waste water. These can cause problems for industrial processes. Foams can increase mechanical wear on pumping systems and problems by blocking sieves and filters, thus reducing water processing efficiency. Foams can also increase the formation of deposits in storage tanks and processing vessels – which have the knock-on impact of increasing cleaning requirements and impact on the growth of bacteria with resultant health issues. Excessive foam discharge is unsightly and may have public image issues for a business locally.
There are a wide range of anti-foaming agents available – many from the GlenFarrow trade showroom and stores – these include alcohols, silicones, stearates, glycols and insoluble oils – all of these work by being low viscosity chemicals that cause the air bubbles to rupture and therefore breakdown surface foam. Selecting the correct chemicals and levels of dosage can have a significant impact on the efficiency of water treatment works.
Waste Water Chemical Treatments and Green Solutions
Most water treatment facilities that use chemical treatment to remove suspended solids depend on either settlement or flotation. Plant design will depend on the nature of effluent – however settlement strategies are most commonly used for the removal of heavy solids, most commonly seen in manufacturing industries, while flotation techniques are more suitable for the removal of oils and fats- that are more commonly seen in the food processing sectors.
A further deciding factor in the most appropriate combination of coagulants and flocculants is the environmental impact of the chemicals to be used. The GlenFarrow team will be able to advise on the best solution.
Green solutions increasingly bio sourced coagulants and flocculants are becoming more common and these can help to impact on an organisation’s green credentials.
GlenFarrow will design complete waste water systems, undertake waste water testing and provide the necessary chemicals- our experienced team will advise on the best solution to meet your needs, legislative, regulatory, environmental requirements to meet day to day business needs
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