We calculate the wastewater volume and the organic load, plan a grease trap for the kitchen, and sort out the documents that the municipality and the environmental service require. We work in Riga and the Riga region; send a request and we will contact you within 5 minutes of receiving it.
Why a household plant isn't enough for a business
In a private house, the daily volume of wastewater is fairly even. In a business it fluctuates: in a café most of the water comes at lunchtime, in a guest house at weekends and in summer, in an office on weekdays, while at weekends the flow almost stops. The bacteria in the plant need food and oxygen without big swings, so it is precisely the peaks and the pauses that determine the choice.
Manufacturers state a plant's capacity in two figures: the hydraulic load (m³ per day) and the organic load (kg BOD5 per day). For a four-person plant, these are about 0.6 m³ and 0.24 kg BOD5 per day, i.e. 60 g BOD5 per population equivalent. For a business, we calculate the two figures separately, because kitchen wastewater is much more concentrated than, for example, shower water in a guest house.
In the calculation we take into account:
- water use from the meter (if the building is already in use, this is the most accurate source);
- the number of seats, beds and staff, the working hours and the season;
- the kitchen: dishwashing, grease, food waste;
- laundry and the disinfectants used for cleaning;
- pauses (closed weekends, the winter season for a guest house).
If the calculation shows that the peak is much higher than the average, we plan a plant with spare capacity or an equalisation tank in front of it, so that an hourly peak doesn't wash the sludge out of the settling tank.
Kitchen and grease: a grease trap before the plant
Grease and oils coat the activated sludge and stop the bacteria from getting oxygen. Manufacturers' instructions list grease and oils among the substances that shouldn't enter the plant in large quantities. That's why, for a café, canteen or guest house with a kitchen, we install a grease trap before the biological plant on the kitchen wastewater line only; toilets and showers don't pass through it.
The grease trap must be cleaned regularly; how often depends on its volume and the number of meals prepared. Cleaning can be combined with the plant's maintenance (see grease trap cleaning).
A domestic biological plant can only treat industrial wastewater (for example, from food production or a car repair shop) if its composition is close to that of domestic wastewater. The manufacturers' passports say so too. If in doubt, a wastewater analysis or separate pre-treatment is needed first.
Documents for a business plant
A factory-made plant with a capacity of up to 5 m³ per day is a decentralised sewage system. It is entered in the municipal register, serviced at least once a year (unless the manufacturer's documentation states otherwise), and within a month of each service the owner submits a copy of the document confirming the maintenance to the register keeper.
In Riga, plants that discharge treated water into the environment must have samples tested in an accredited laboratory once every two years. The effluent must meet the limit values in the binding regulations: BOD5 25 mg/l, COD 125 mg/l, suspended solids 35 mg/l, total phosphorus 1 mg/l, total nitrogen 10 mg/l. That is why, for Riga, we choose a plant based on the manufacturer's test results for nitrogen and phosphorus as well, not just BOD5.
If the plant's capacity is between 5 and 20 m³ per day and the treated water is discharged into the environment, it is a category C polluting activity: the notification is submitted to the State Environmental Service at least 30 days before the activity starts. From 20 m³ per day, a category B permit is needed. The construction documents are submitted through BIS; the building authority decides their type based on the plant's capacity and the site.
Sources, checked on 30 October 2026: Cabinet Regulation No. 384 of 27.06.2017 (points 3.1, 4.3, 15.3); Riga City Council Binding Regulations No. 66 “On the procedure for providing, recording and monitoring decentralised sewage services” (point 5.5, Annex 1); Cabinet Regulation No. 1082 of 30.11.2010 (point 6, Annex 1 point 8.9, Annex 2 point 6.3). Municipalities in the Riga region have their own binding regulations, and we check them for the specific address.
How we work
- Data and load calculation We ask for the water meter readings, the number of seats or beds, the working hours and a description of the kitchen. From these we calculate the flow in m³ per day and the organic load.
- Site visit We check the groundwater level, the discharge point (infiltration or a ditch), the power supply for the compressor and access for a vacuum tanker.
- Solution and estimate We choose a plant model with spare capacity, a grease trap and, if needed, an equalisation tank or a pump station. The estimate lists each item separately.
- Installation and start-up We install the plant, connect the compressor and the controls, start it up and adjust the air supply to match the load.
- Maintenance schedule For a business plant, the maintenance frequency is set by the load: often twice a year or more. After each service we issue a document for you to submit to the register.
How much does it cost?
The price of a business plant depends on the calculated load, so we give the final amount after the calculation. As a guide, use the published prices for a household plant and for the work (see also prices).
The price depends on the plant's capacity, the grease trap, the discharge solution, groundwater (base and anchoring), the distance from the building and whether a pump station is needed.