Question

What is an activated sludge system and what are the processes that occur in the system? What is the role of "mixed liquor suspended solids"? (hint: draw the system diagram and think about what can be happening)

Answer 1

The activated sludge process is a type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.

The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: An air circulation tank where air (or oxygen) is infused in the blended alcohol. This is trailed by a settling tank (more often than not alluded to as "last clarifier" or "optional settling tank") to permit the organic flocs (the ooze cover) to settle, along these lines isolating the natural slime from the reasonable treated water.

Purpose

In a sewage or industrial wastewater treatment plant, the initiated slime process is an organic procedure that can be utilized for one or a few of the accompanying purposes: oxidizing carbonaceous natural issue, oxidizing nitrogenous matter: mainly ammonium and nitrogen in biological matter, removing nutrients (nitrogen and phosphorus

Process description

The process takes advantage of aerobic micro-organisms that can digest organic matter in sewage, and clump together (by flocculation) as they do so. I t in this way creates a fluid that is moderately free from suspended solids and natural material, and flocculated particles that will promptly settle out and can be evacuated.

The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items:

Aeration tank where air (or oxygen) is injected in the mixed liquor.

Settling tank (as a rule alluded to as "last clarifier" or "auxiliary settling tank") to permit the organic flocs (the slime cover) to settle, in this way isolating the natural muck from the unmistakable treated water.

Treatment of nitrogenous matter or phosphate involves additional steps where the mixed liquor is left in anoxic condition (meaning that there is no residual dissolved oxygen)

The procedure includes air or oxygen being brought into a blend of screened, and essential treated sewage or modern (wastewater) joined with life forms to build up a natural floc which lessens the natural substance of the sewage. This material, which in sound muck is a dark colored floc, is to a great extent made out of saprotrophic microorganisms yet in addition has an essential protozoan vegetation segment chiefly made of amoebae, Spirotrichs, Peritrichs including Vorticellids and a range of other filter-feeding species. Other important constituents include motile and sedentary Rotifers. In poorly managed activated sludge, a range of mucilaginous filamentous bacteria can develop including Sphaerotilus natans which produces a sludge that is difficult to settle and can result in the sludge blanket decanting over the weirs in the settlement tank to severely contaminate the final effluent quality. This material is often described as sewage fungus but true fungal communities are relatively uncommon.

The combination of wastewater and biological mass is commonly known as mixed liquor. In all activated sludge plants, once the wastewater has gotten adequate treatment, overabundance blended alcohol is released into settling tanks and the treated supernatant is kept running off to experience further treatment before release. Some portion of the settled material, the ooze, is come back to the leader of the air circulation framework to re-seed the new wastewater entering the tank. This fraction of the floc is called return activated sludge (R.A.S.).

The space required for a sewage treatment plant can be reduced by using a membrane bioreactor to remove some wastewater from the mixed liquor prior to treatment. This outcomes in a more focused waste item that would then be able to be dealt with utilizing the initiated muck process.

Many sewage treatment plants use axial flow pumps to transfer nitrified mixed liquor from the aeration zone to the anoxic zone for denitrification. These pumps are often referred to as internal mixed liquor recycle pumps (IMLR pumps). The crude sewage, the RAS, and the nitrified blended alcohol are blended by submersible blenders in the anoxic zones with the end goal to accomplish denitrification.

Objective of Waste Water Treatment:

The objective of municipal and industrial waste water treatment is to extract pollutants, remove toxicants, neutralise coarse particles, slaughter pathogens with the goal that nature of released water is enhanced to achieve the admissible dimension of water to be released into water bodies or for farming area.

Treatment of water in this manner goes for decrease of BOD, COD, eutrophication and so on of getting water bodies and anticipation of bio-amplification of poisonous substances in evolved way of life.

Steps Involved in Waste Water Treatment:

1. Preliminary Treatment.

Screening:

In this treatment flotsam and jetsam, net solids, coarseness, oil and oil are expelled by going waste water through screens, coarseness chambers and skimming tanks.

2. Primary Treatment:

Primary treatment of sewage removes 60% suspended solids, 30% COD, 35% BOD, 10% P and 20% total nitrogen.

It includes the following processes:

(i) Sedimentation:

About half suspended solids can be expelled by gravitational settling under tranquil conditions.

(ii) Mechanical Flocculation and Coagulation:

Fine suspended solids and colloidal particles are removed by passing waste water through clariflocculator and using coagulants like alum and poly-electrolytes.

(iii) Neutralisation:

Exceptionally acidic and antacid waste waters are killed by lime slurry or NaOH and H2SO4 or CO2respectively.

3. Secondary (Biological) Treatment:

The dissolved and colloidal organic matter in waste water/sewage is removed by aerobic or anaerobic processes. Very acidic and basic waste waters are killed by lime slurry or NaOH and H2SO4 or CO2respectively.

Then the sludge obtained in these aerobic processes, together with that obtained in the primary sedimentation tank, is subjected to anaerobic digestion in the sludge digester. Secondary treatment removes about 80% COD, 90% BOD, 30% P, 50% total N and oil, grease, phenol, grit, scum etc.

4. Tertiary Treatment:

Tertiary treatment is the final treatment meant for abolishing the secondary effluents and removal of fine suspended solids, traces of organics and bacteria. The sewage profluent from optional treatment plant is brought into a flocculation tank where lime is added to take out calcium phosphate.

The solution then enters the NH₃ stripping tower. Nitrogen present in waste water exists as NH⁺₄ which is converted to gaseous ammonium ion at high pH(ll). Phosphorus is expelled by including ferric chloride or aluminum sulfate. The staying natural materials are expelled by desalination, particle trade lastly chlorination is utilized for cleansing.

The poisonous, non-biodegradable synthetic compounds in mechanical waste water can be evacuated by adsorption (on initiated charcoal), particle trade, ultra-filtration, switch assimilation and electrodialysis.