Effluent Treatment for the Food Industry
Water represents a dual cost burden for a food-processing company. It must satisfy high hygienic demands for the process and also have an absolutely neutral taste.
|Water as product constituent and cleaning agent|
|Cut costs due to automated measuring and registration|
|Types of effluent in food industry|
|Description of effluent treatment|
Effluent is even more expensive for the majority of companies. Due to continually increasing charges, it is worthwhile for many companies to construct their own sewage treatment plant.
Water as product constituent and cleaning agentWater is required to make a large number of products. This water remains in the product.
This represents the first task in production engineering: How much of the water which flows into the company does not flow out, i.e. must not be calculated for effluent? The measurement of fresh water and effluent can help in this case.
However, most water is used for cleaning purposes.
Alkali with a concentration of up to 2.5% at a temperature of up to 90°C is the normal medium. Cold beverage waste, mostly acidic, is perfect for neutralization in this case. However, water also transports all smaller impurities out of the company. oxygen demand (BOD) or chemical oxygen demand (COD), the number of mean resident values formed therefore are used as a calculation basis. Peaks in individual values are often "punished" severely. Proof that effluent was always within limits is prescribed by law. Automation of measurement and registration can substantially reduce the otherwise high personnel expenditure and lead to cost savings during negotiations with the responsible authorities.
a) Effluent containing practically no solids, e.g. at drinks manufacturing companies and dairies
b) Effluent containing solids, e.g. at sugar factories or meat companies
Effluent according to a) is normally collected and, if necessary, neutralized in a mixing and equalizing tank before it enters the sewage treatment plant. This step takes place in the overwhelming majority of cases on the company's premises in order to avoid peak pH and temperature values or relieve the burden on the company's own sewage treatment plant. Municipal sewage treatment plants normally insist on compliance with the limit values. The effluent is therefore already treated prior to the measurements which are used to calculate the charges. The objectives are pH neutrality and discharge temperatures below 35°C.
The solids in effluent according to b) produce a high COB of up to 50 kg/l. These solids must be hydrolyzed before they enter the biological treatment stages. The solids are hydrolyzed as organic acids, i.e. metabolized, by micro-organisms during a two-stage anaerobic pre-treatment process.
The contaminants from both types of sewage are then reduced to carbon and nitrogen in the two-stage, biological anaerobic sewage treatment plant. Since biological phosphate precipitation is mostly insufficient, chemical precipitants are added during the second stage. Sludge is produced in addition to the liquid phase. Some of the biomass thus produced is used in a cycle process to "feed" the micro-organisms in the aerobic stages and thus keep the process going.
The biogas that is also produced can be used, for example, for energy purposes in a CHP station.
At the end of the process, the cleaned water is discharged into an outfall (mostly a river).
The excess sludge is stabilized, dehydrated and burned.