Understanding the 2 types of sludge and ways to easily handle sludge

    October 11, 2021

    Handling sludge can become a significant headache in sewage treatment problems if the correct treatment plant is not in place. Whichever the treatment process and design, sludge is a by-product, the quantity may differ, but sludge will be present. Different treatment designs create Type1 or Type 2 or both types of sludge; in general, there are two types of sludge. In this blog, let us understand sludge and ways to handle them.

    What are sludge and the types?

    Sludge is accumulated in sewage treatment plants as a by-product of the treatment process and looks like a semi-solid slurry. They are typically two types of sludge, and they are primary and secondary sludge.

    Primary Sludge

    The primary treatment involves gravity sedimentation and flotation that remove approximately half of the solid material entering this stage. Solid material (both organic and inorganic) that settles out during this stage of treatment is drawn from the bottom and constitutes the primary sludge.

    In treatment plants, the operator skims the floating material (oil, grease, wood and vegetable matter) from the water surface during the primary treatment, is disposed of separately and does not become part of the primary sludge. In most of the cities disposing of the primary sludge is becoming difficult with strict regulations. The authorities are imposing strict rules to handle the primary sludge responsibly.

    Secondary Sludge

    The secondary treatment is a carefully and accelerated biological process. Naturally occurring microorganisms are used to degrade (breakdown or digest) suspended and dissolved organic material in the wastewater—the material converts into carbon dioxide and releases into the atmosphere and microbial cell mass.

    In secondary sedimentation tanks, the microbial cell mass settles to the bottom and is removed through pumps. The primary organic material is called secondary sludge. Some treatment plants utilise a small portion of the secondary sludge as inoculum, and the treatment is known as ACTIVATED SLUDGE PROCESS. The rest of the sludge is sun-dried and used as fertilisers.

    In OxyO, the design of the sewage treatment plants is such that you do not get the primary sludge. There is a Bar screen to remove the non-biodegradable materials like plastic bags, Napkins etc. After that, the treatment process begins at the first tank itself. The consortium of microorganisms digests the organic materials, which are bio-degradable in the first tank. Then sludge floats in the settling tank and is skimmed once a month or according to the quantity produced. The sludge is dried in the sun and is used as a fertiliser in the gardens. In some treatment plants, the sludge quantity produced is so low that they have not removed the sludge for even two years. The appearance of the sludge may look huge in amount but once dried, they are minimal. The sludge does not produce any foul odour, which is another concern to the clients.