Bacteria for biological treatment plants - do you need them?

How bacteria work in a BIO plant

In a BIO plant, aerobic bacteria treat the wastewater. They need food, which the wastewater provides, and oxygen, which the compressor supplies. Together with particles from the wastewater they form activated sludge, which renews itself all the time: some of the sludge keeps growing, and the surplus is removed periodically.

So there are “enough” bacteria as long as the plant receives wastewater, the compressor runs and nothing that kills bacteria gets into the sewer. If any of these conditions is not met, a bacterial product won't solve the problem.

What manufacturers say about bacteria for BIO plants

The conclusion is simple: if the manufacturer recommends bacterial products, use them as instructed; if not, the money is better spent on timely maintenance. For data on other manufacturers, see BIO plant comparison.

When bacteria really help

• When starting up a new plant, if the manufacturer's instructions provide for it.
• After the surplus sludge has been pumped out. The AQUABLOC manual, for example, requires it to restore the bacterial flora.
• After a long period of inactivity, when the plant has received no wastewater for weeks, if the manufacturer recommends it.
• If a large dose of chemicals has got into the sewer and the sludge has suffered - together with maintenance, not instead of it.

When bacteria won't help

Most often a BIO plant “doesn't work” not because of a lack of bacteria but for a technical reason:

• the compressor is not working or its membrane is worn, and without air the aerobic bacteria cannot work;
• the airlifts or the solids bag are clogged;
• too much sludge has built up in the plant, and it leaves with the treated water;
• rainwater, pool water or hot water is flowing into the plant;
• the plant is too small for the actual water consumption.

If the plant raises an alarm, smells or the discharged water is cloudy, it needs maintenance first. For what the alarms mean, read biological plant alarm; for the work itself, see BIO plant maintenance.

What must not go down the drain

Manufacturers' instructions list what must not get into the plant:

• oils and lubricants in high concentrations, fats;
• paints, varnishes, solvents and acids, including battery acid;
• expired medicines, pesticides and other toxic substances;
• plastic, rubber, textiles, hygiene products, wet wipes, paper towels;
• rainwater, pool water and water hotter than 40 °C.

Ordinary washing and cleaning products may be used in moderation. The AUGUST passport says so directly.

How to check whether the sludge is alive

1. Take a sample While the compressor is running, take 1 litre of the sludge mixture from the aeration chamber in a clear container.
2. Wait 30 minutes Let the sludge settle; there should be a clear line between the sludge and the water.
3. Read the amount AUGUST specifies 300–600 ml of sludge per litre (optimally 400–500 ml), PURA 200–400 ml. If the sludge does not settle or there is too much of it, the plant needs maintenance.

Other warning signs: brown foam, floating sludge in the settling chamber, a strong smell. In such cases the AUGUST passport advises contacting a service provider.

Bacteria for a septic tank

A septic tank is not an aerobic system: it has no compressor, and sediment builds up in any case. Septic tank products may be advertised as reducing smells or sediment, but none of them cancels the minimum pumping frequency set by the municipality. In Riga it is at least once a year. Read more in how often to pump a septic tank.