Effluent Treatment Plant

WASTEWATER TREATMENT PROCESS

Coarse screens or bar racks  :

(1) removes large objects, rags, debris ; (2) protects downstream pumps, valves, pipelines ; (3) cleaning may be accomplished manually or mechanically ; (4) mechanically cleaned bar racks typically used instead of coarse manually cleaned screens ; (5) bar rack is inclined to facilitate , cleaning ; (6) approach velocities should ensure self-cleaning, but not dislodge solids.

Aerated Grit Chamber:

Inert dense material such as sand, broken glass, slit and pebbles, etc is called grit. If these materials are not removed from the waste water they abrade pumps and other mechanical devices, causing undue wear. In addition they have a tendency to settle in corners and bends, reducing flow capacity and ultimately, clogging pipes and channels. In aerated grit chamber the shearing action of the bubbles is supposed to strip the inert grit of much of the organic material that adheres to its surface.

Equalization:

Equalization is not a treatment process but a technique that can be used to improve the effectiveness of both secondary and advanced wastewater treatment processes. Equalization is usually achieved by constructing large basin that collect and store the waste water flow from which the waste water is pumped to the treatment plant at a constant rate with a average temperature. Addition of aeration at equalization tank also reduces Temperature, TSS, BOD and COD.

Flocculation:

Flocculation is a process where colloids come out of suspension in the form of floc or flakes. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system there is no formation of a cake since all the flocs are in the suspension. Flocculants, or flocculating agents (also known as flocking agents), are chemicals that promote flocculation by causing colloids and other suspended particles in liquids to aggregate, forming a floc. Flocculants are used in water treatment processes to improve the sedimentation or filterability of small particles. Many flocculants are multivalent cations such as aluminum, iron, calcium or magnesium. These positively charged molecules interact with negatively charged particles and molecules to reduce the barriers to aggregation. In addition, many of these chemicals, under appropriate PH and other conditions such as temperature and salinity, react with water to form insoluble hydroxides which, upon precipitating, link together to form long chains or meshes, physically trapping small particles into the larger floc.

10 Ca2+ + 6 PO43- + 2 OH- ↔ Ca10(PO4)*6(OH)2 ↓

Ca(HCO3)2 + Ca(OH)2 à 2CaCO3 ↓+ 2H2O

Al3+ + HnPO43-n ↔ AlPO4 + nH+

Fe3+ + HnPO43-n ↔ FePO4 + nH+

Clarifier (LAMELLA)/Sedimentation Tank:

¨  Removal of SS, BOD and COD about 50-55% at primary clarification.

¨  Reduces space but surface area increases.

¨  Solid Particle is settled easily by Cross flow through the inclined surface

¨  Less Power requirement

¨  Easily sludge removed due to downward flow into hopper.

¨  More effective than normal clarifier.

Fluidized Media Reactor (FMR):

The FMR technology is a single tank design unit; incorporating

  • A bar screen,
  • A specially designed tank with synthetic media,
  • A lamella settler, and
  • A chlorine contact tank.

Advantages:

¨  The main objective of adding this media is to make available more surface area for bacteria to grow on.

¨  The FMR media material allows biomass concentration of 20 – 40 Kgs/m3 material.

¨  High concentration of biomass enables reduction of aeration tank and in turn reduction in overall cost.

¨  As all units are placed inside a single tank, it saves space and also increases operational ease, Increases the specific volumetric capacity of activated sludge tanks, Controls biomass activity.

¨  Reduced power and operating costs

¨  No Sludge recycle

¨  No moving parts, less maintenance

Activated sludge process/Aeration:

Activated sludge process derives its name from the biological mass formed when air is continuously injected into the wastewater. In this process microorganisms are mixed thoroughly with the organics under conditions that stimulate their growth through use of the organic food. As the microorganisms grow and are mixed by the agitation of the air, the individual organisms clump together to form an active mass of microbes (biological floc) called activated sludge.

C5H7NO2+5O2= 5CO2+2H­2O+HN3+Energy

The technique consists of 3 different systems:

  1. A biological reactor - using a suitable biomass for settling,
  2. An aeration system to provide the necessary oxygen for the biomass,
  3. A separation facility, where the purified water is separated from the biomass through settling.

Adsorption (PAC, Natural Adsorbent)

Many industrial wastes contains organic, which are refractory and which are difficult or impossible to remove by conventional biological- treatment processes.  These materials can frequently be removed by adsorption on an active solid surface. When a solid- fluid containing system of operation is used to treat a fluid stream on an industrial scale, one of the following characteristics has usually been responsible for its selection as the most economical methods for treatment.

1.       High selectivity of the adsorbent.

2.       High concentrating power of  the adsorbent, related to the   Selectivity

3.       Chemical instability of the adsorb ate, restricting it to temperatures  unsuited for other separation

4.       Fluctuation or intermittent supply of the fluid feeds.

5.       Less space need & Lower capital investment.

6.        Simple design & Easy operation of the equipment.

7.        Efficient removal of organic waste constituents.