What is septicity in sewage & sludge?

Septicity in sewage & sludge

What is septicity in sewage & sludge? Sewage stinks! Or it would if left untreated. When the micro-organisms have used up all the oxygen and nitrates it has become anaerobic. Then proteolytic bacteria in the sludge react with compounds containing sulphur to form sulphides, (H2S). In other words, H2S is produced by the breakdown of organic material in the absence of oxygen. (In Victorian times it was fashionable to take children to the local gas works to smell the “health-giving” fumes.

Why is this important?

1. The smell!
2. Hydrogen sulphide has corrosive effects on metals and concrete. It reacts with water to form sulphuric acid, in the presence of certain oxidising bacteria.

Dealing with the smell

The micro-organisms need to be inhibited to prevent the septicity of sewage or sludge.

PH control

Sewage smells especially when it is anaerobic and septic. Sludges tend to have a greater density of microbes that also smell. The odours are classified as acidic – hydrogen sulphide and organic sulphides, and volatile – fatty acids like acetic acid, propionic and butyric acids.

H2S and organic sulphides smell even when very small quantities are released. This is especially true when the medium is acidic – and is much of sewage, because of the fatty acids. When the pH is raised above the neutral level of 7 then there is a higher threshold to the smell – but it lasts longer.

When the pH rises above 8.5, then the odours associated with an alkaline medium take over. The problem of malodourous sewage is not resolved.

Aeration

Adequate aeration does help to reduce the problem of odours – but when the sewer is well filled anaerobic reactions take place and H2S is produced. If the sewages is slow-flowing it is more likely to become blocked and aeration will be less.

Cleaning of tanks and pipes

Many of the tanks used for sludge treatment are conical in shape this means the sludge settles in the bottom of the cone and can be easily removed and the tanks can be completely cleaned.

Chemical treatments for septicity

Treatment options for septicity generally include adding oxidants such as hypochlorite, hydrogen peroxide and potassium permanganate. The addition of iron salts – they react with the sulphides to form insoluble iron sulphide. Controlling the pH and converting H2S to HS and S2.

How Enduramaxx tanks are used

Our rotationally moulded plastic bunded chemical tanks are designed to store and holding of chemicals used to treat sewage and sludge safely. Open top conical tanks are available with a shallow base which are also used as aeration tanks and for algae wastewater treatment installations. Our full range of tanks from effluent treatment and clarifier tanks to sludge conditioning tanks are available here.

For further information, do give us a ring on 01778 302873.

Main image Istock