SEWAGE TREATMENT

What is sewage?

Sewage is the wastewater generated from domestic operations (house hold/offices/ commercial complexes/ hotels/ etc.)

Domestic operations include:

• bathing

• Clothes washing

• Kitchen (vegetable washing/ utensil washing)

• Toilets/ urinals

Why sewage need to be treated?

•To protect public health

• To prevent disease causing environment

• To prevent pollution of water bodies into   which sewage is being discharged

• To reuse treated sewage there by reducing the requirement of fresh water

WATER REQUIREMENT

Water usage                                                                      Quantity

                                                                                   (L/head/day)*

Drinking                                                                                                   3

Bathing                                                                                                      30

Toilets/Flushing                                                                                  45

Laundry                                                                                                     30

Kitchen/ Dish washes                                                                       22

Leakages                                                                                                   15  

Total                                                                                                             145

Sewage quantity

about 80% of water supplied finds its way into drain

Hence sewage quantity can be assumed as follows:

For residences                                           : 120 l/head/day

For industries/ offices/                        : 40 l/head/day

Commercial establishments

For hotels                                                     : 150 l/room/day

Restaurants                                                 : 15 l/head/day

For hospitals                                               : 200 l/bed/day

TYPICAL SEWAGE CHARACTERISTICS

ALL PARAMETERS EXCEPT pH ARE IN mg/l

TERMINOLOGY OF SEWAGE TREATMENT:

BOD IS THE AMOUNT OF OXYGEN REQUIRED TO OXIDISE ORGANIC MATTER USING BACTERIA UNDER STANDARD CONDITIONS. THIS INDICATES THE AMOUNT OF ORGANIC MATTER PRESENT IN THE WASTEWATER

MLSS IS MIXED LIQUOR SUSPENDED SOLIDS. IT INDICATES AMOUNT OF BACTERIA PRESENT IN THE SYSTEM

DO IS DISSOLVED OXYGEN PRESENT IN AERATION TANK. DO IS REQUIRED FOR BACTERIA FOR RESPIRATION

F/M RATIO IS THE RATIO BETWEEN KG FOOD (BOD) AVAILABLE TO KG BACTERIA (MLSS)

ORGANIC MATTER IN WASTE WATER IS MEASURED IN TERMS OF BOD (BIOLOGICAL OXYGEN DEMAND) OR COD (CHEMICAL OXYGEN DEMAND).

OBJECTIVE OF BIOLOGICAL TREATMENT OF SEWAGE :

• MAIN OBJECTIVE IS TO REMOVE ORGANIC MATTER FROM WASTEWATER IN A NATURAL WAY WITHOUT USING TOXIC CHEMICALS

BIOLOGICAL TREATMENT CAN BE

AEROBIC WHICH REQUIRES OXYGEN FOR THEIR ACTIVITY

OR

ANAEROBIC WHICH DOES NOT REQUIRE OXYGEN AND PRODUCES METHANE AS A BY-PRODUCT FOR POSSIBLE USE AS ENERGY

AVAILABLE TECHNOLOGIES

AEROBIC                                                             ANAEROBIC

1. CONVENTIONAL ASP            

1. FIXED FILM REACTOR

2. EXTENDED ASP                                                   1. FLUIDISED BED REACTOR

3. TRICKLING FILTER                                           2. UPFLOW ANAEROBIC

4. ROTATING BED CONTACTOR      3. SLUDGE BED REACTOR

5. SUBMERGED AEROBIC FIXED FILM

     REACTOR

6. FLUIDISED AEROBIC BED REACTOR

7. HIGH RATE SUBMERGED MEMBRANE

   SOME BASICS OF

BIOLOGICAL TREATMENT

BACTERIAL GROWTH

STARTS WITH A SINGLE BACTERIUM (2 X 10-9 g) WITH 30 MINUTES DOUBLING TIME

 

IN BIOLOGICAL TREATMENT…..

…. MICROORGANISMS CONSUME SOLUBLE AND COLLOIDAL ORGANIC COMPOUNDS PRESENT IN WASTEWATER.

MICROORGANISMS GROW AND SUBSEQUENTLY SEPARATED FROM THE WASTEWATER WHICH HAD THE BOD REMOVED.

CO2, H20

NEW CELLS

ORGANIC MATTER

 

FLUIDISED MEDIA REACTOR (FMR)

A high rate aerobic biological treatment system

Basic principle

Flock forming organism’s form clusters or attach to available surfaces. The FMR carrier material allows high biomass concentrations per cubic meter of material, which:

• Increases the specific volumetric capacity of activated sludge tanks
• Controls biomass activity
• Reduces operating cost

FMR SCHEME

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.

The bar screen removes larger floating matter and suspended particles. Screened sewage flows into the FMR tank, which contains the FMR media. The FMR media significantly increases the surface area for bacterial growth. Air is supplied through fine diffusers. Bacteria oxidize the organic matter present in the sewage. Oxidized sewage overflows in the lamella settler. Suspended particles in the treated wastewater settle, with a part of the settled sludge sliding back to the aeration tank. The lamella plates provide larger surface areas, thus reducing the settling tank size. Treated water overflows into a chlorine contact tank, wherein the treated water is disinfected by dosing hypochlorite solution through an electronic dosing system.

Advantages using FMR

• Significant reduction in space requirement due to high surface area & loading rate of FMR media.
• Reduced power and operating costs
• No Sludge recycle
• No moving parts, less maintenance

Advantages over FAB

• FMR has fewer tanks than FAB. Hence, it is more compact
•  FMR occupies less area than FAB (FMR requires 25% less area than FAB)
•  FMR adopts lamella technology for settling which is more efficient and superior than tube settler of FAB
•  Lamella plates can be easily cleaned while the unit is in operation. Tube settler cannot be cleaned online
•  Tube settlers are more prone to clogging
• Advantages over ECO-CELL
• •FMR is a biological process which is close to the nature. ECO-CELL is a physico-electro-chemical process requiring dosing various chemicals like polymers, salt and consumable electrodes. Life of electrode is 2 to 3 months approx.
•  FMR does not alter TDS level of sewage whereas ECO-CELL increases TDS of the treated sewage which is not good for the plants
•  As ECO-CELL depends only on chemical process for BOD/COD reduction, it cannot efficiently remove them and hence cannot produce high quality treated sewage
•  The electrodes get scaled and become inefficient in its performance requiring very frequently maintenance.

FMR is best suitable when

• Designing a new waste water treatment plants when operating cost & space  are constraints
• Upgrading of existing waste water treatment plants
• Operate plants in low temperature areas
• Reduce bulking problems in existing treatment plants

Applications of FMR

1. Decentralized compact sewage treatment plants for Residential complexes, 

      / Hotels / Commercial Center’s / Office Premises / Industries and Rural  

      Communities.

II)  Industrial wastewater treatment from:

• Food & Beverage
• Textiles
• Pulp & Paper
• Chemicals
• Pharmaceuticals
• Petro-Chemicals
• Dairy Production

PROCESS DETAILS

Bar Screen:

Raw sewage from the source is usually received into the bar screen chamber by gravity. Screen provided will remove all floating and big size matter such as plastic bottles, polythene bags, glasses, stones, etc., which may otherwise choke the pipeline and pumps.

Oil and Grease Trap (Civil Construction)

If the sewage generated includes maximum quantity from kitchen and canteen, there is a possibility of higher concentrations of oil and grease in the raw sewage.  It needs to be removed before biological treatment as it otherwise may cause problems for biological treatment. Usually, a small civil construction tank with a baffle wall and slotted oil pipe skimmer is provided. The oil and grease removed by gravity floats to the surface, which is removed by the oil skimmer (by client).

Equalization Tank (Civil Construction)

Usually, sewage generation is more during morning hours and evening hours. Visually no sewage is generated during night hours. Any biological system needs constant feed for bacteria to work efficiently. Hence, it is important to put an equalization tank to collect the excess flow during peak hours and feed sewage in lean hours. A typical equalization tank has a capacity of 8 – 12 hours of average flow rate. The tank is generally of civil construction by client. Provision of air grid is to be made for thoroughly mixing the sewage to make it of homogenous quality and to keep the suspended matter in suspension and to avoid septic conditions.

Transfer of Sewage

Our scope starts from transfer of sewage from Equalization Tank to FMR tank.  The distance of transfer should not exceed beyond 5 meter.  The transfer pump is non-submersible type for this application.

• The pump should not run dry and Client to ensure sufficient sewage is available in the Equalization Tank.

Fluidized Media Reactor (FMR)- Civil Tank Construction with Media.

Fluidized Media Reactor (FMR) as the name indicates consists of floating media of various shapes and sizes. The main objective of adding this media is to make available more surface area for bacteria to grow on, thereby maintaining and retaining maximum possible bacterial population in a limited volume. The FMR media material allows biomass concentration of 20 – 40 Kgs/m3 material. Thus, FMR consists of combination of biomass in attached as well as suspended form. High concentration of biomass enables reduction of aeration tank and in turn reduction in overall cost. Volume of the media shall vary from 6 to 25 % based on the concentration of organic matter.

Another main feature of the FMR is its compactness. The FMR consists of biological system for removal of organic matter (BOD, COD), lamella for clarification and chlorine contact tank for disinfection. As all units are placed inside a single tank, it saves space and also increases operational ease.

In FMR, raw sewage enters at the top of the tank. Air is introduced at the bottom of the tank through fine bubble diffusers. Media will be in suspension because of the turbulence created by the air.  The bacteria required for the oxidation of the organic matter is attached to the media and some part is suspended in the tank.  After oxidation, the bacteria grow in number and need to be separated from the aeration tank liquor. The lamella section inside the FMR helps in clarification and separation of the bacteria (sludge) and clear overflow flows into chlorine contact tank. Lamella plates helps in increasing the settling area and removing the particles effectively in a smaller plan area. In chlorine contact tank, Sodium hypo Chlorite (NaOCl) is added for disinfecting the clarified sewage. Baffle plates are provided to make better contact. The chlorinated treated sewage then flows out of FMR either for further treatment or for disposal.

Treated Water Collection Tank:

The treated water collection tank can be of civil construction by client in case required. The treated water can be collected either from the chlorination chamber in Scheme I or from Activated Carbon Filter in Scheme II.

Sludge:

The sludge from the Clarifier to be removed from the bottom of the Clarifier once in a day by client and transferred to sludge drying bed either by gravity or through pump depending on site condition.  Before starting the De-sludging, shut off the aeration for 30 minutes and allow the sludge to concentrate at the bottom.

After concentration, the bottom sludge valve can be open to drain the required quantity of sludge. An air scour pipe is provided to dislodge any media choking the drain outlet. Open the air scour valve for short time to remove the clog.

FLOW DIAGRAM

NEW GENERATION

PACKAGE SEWAGE TREATMENT PLANT

(NG PSTP)

IEI SCOPE OF SUPPLY

 

 

 

1. Introduction

The INDION New Generation PSTP is the most compact “all in one” system available. The civil works are minimal, consisting of a flat concrete support slab the plan area of the unit constructed is 1.4 meters below the invert of the incoming pipe.  The units are fully covered preventing noise and fly nuisance.  It is a modular unit that lends itself to future expansion or relocation.

2. Treatment

Sewage Transfer

Ion exchange scope starts with transfer of sewage .The sewage transfer pump will be installed near equalizations tank and the transfer distance is not recommended more than 10 meters.

Primary Settlement

The plant is designed for receiving raw sewage and settling the gross solids without recourse to mechanical means.  It incorporates Lamella or parallel plates to enhance efficiency and utilization of space. The Primary Settlement zone reduces the Suspended Solids by 75% and the BOD by 25% to 30%.  This zone is relatively maintenance free and contains no moving mechanical or electrical devices.  Lockable GRP covers with easy man access and sufficient ventilation are provided. The recirculation from the Aerator and the return of humus sludge into the primary settlement zone inhibits the settled effluent from becoming anaerobic, which prevents bad odor.

Aerobic Treatment

The settled sewage is treated by means of an efficient and compact system (the Aerator Biozone) requiring minimal power input and maintenance.  It is a combined fixed film reactor and active aeration system mounted on a horizontal shaft.  The rotational media is a spiral formation enclosed in an outer drum to provide active aeration, intense surface area and net hydraulic lift. The Biozone is self-cleansing and no extraneous pumping or sludge returns are required. For process efficiency it is, in effect, a plug flow system.

Final Settlement

The Final Settlement or Humus Tank is a discrete compartment denying ingress of untreated or partially treated liquor.  The design is similar to the Primary Settlement Tank on an upward flow basis.

Sludge Storage

Sludge Storage is provided in the base of the units.  Depending on the load applied there is approximately 12 weeks capacity provided. De-sludging can be carried out by suction tanker.

3. Material of Construction
Tankage

The proposed plant INDION NG PSTP 4000 is a single tank system and can be supplied in modules. The outside of each tank is steel reinforced GRP and can be free standing All internal surfaces in contact with sewage are GRP. Lifting hooks are provided for easy transportation. The tank and internal components are accessed by a series of lockable GRP covers capable of being lifted by one person.

Mechanical

The shaft supporting the media is manufactured from EN 8 steel and has a variable diameter.  It is driven through a helical gear type reduction gearbox with an output speed of 6 RPM. Each section of shaft is coupled by a duplex chain coupling encased in a chain guard with a grease nipple. The shaft is supported by roller bearings in Plummer blocks fitted with double lip seals and grease nipples.  The unit has just one drive train. A grease gun with extended grease hose is mounted in the motor Gearbox compartment.

Electrical

The main motor in the unit is 3.728 kW (3 phase, 415 Volts power supply). A sludge return pump (Single phase, 220-240 Volts power supply) 0.87 kW is also provided which runs intermittently for 2 minutes in every half an hour. A single control box is mounted in the motor / gearbox compartment and accessible from the surface. It contains all the electrical controls and is to IP 55 standards. 

INDION ® Sodium Hypochlorite Dosing System model CDS 1      

Dosing of Sodium hypochlorite helps in disinfecting the water and making it suitable and safe for gardening.  The chemical is dosed by means of an electronic dosing pump wherein a facility is available for manual control of stroke length and stroke frequency.

NGPSTP Summary

• All-in-one Package Sewage Treatment Plant
• Probably the Most Compact in the World
• Very Simple to Operate
• Easy to Maintain
• Low Operating Cost
• Modular
• Mechanically Reliable
• Efficient Process
• Simple maintenance

 DISINFECTION OF WASTE-WATER

Like drinking water, liquid wastewater effluent is disinfected. Unlike drinking water, wastewater effluent is disinfected not to directly (direct end-of-pipe connection) protects a drinking water supply, but instead is treated to protect public health in general. This is particularly important when the secondary effluent is discharged into a body of water. Chlorination for disinfection follows all other steps in conventional wastewater treatment. The purpose of chlorination is to reduce the population of organisms in the wastewater to levels low enough to ensure that pathogenic organisms will not be present in sufficient quantities to cause disease when discharged.Disinfectants kill present unwanted microorganisms in water. There are various different types of disinfectants:
Disinfection is carried out by-

• Chlorination
• Ozonization
• UV Sterilization

 Chlorination

• To oxidize dissolved organic matter
• To destroy algae and pathogenic bacteria.

   Chlorination can be carried out by:

• Chlorine  gas/liquid
• Sodium hypochlorite solution
• Bleach liquor
• Chlorine in water dissociates to form hypochlorous (HOCl) and hydrochloric (HCl) acids.
• HOCl dissociates to give hypochlorite (OCl) and hydrogen (H) ions.
• pH     < 5       free chlorine exists
• pH  5 – 8       HOCl predominates
• pH     > 8       OCl   predominates.
• pH   5 – 8       is desirable as HOCl is 80% and more effective than OCl ion
• To be effective both dosage and contact time are important.
• Free residual chlorine (FRC) of 0.1 – 0.2 mg/l ensures absence of pathogenic bacteria.

 Chlorine dioxide disinfection:-

ClO₂ is used principally as a primary disinfectant for surface waters with odor and taste problems. It is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. ClO₂ penetrates the bacterial cell wall and reacts with vital amino acids in the cytoplasm of the cell to kill the organisms. The by-product of this reaction is chlorite. Chlorine dioxide disinfects according to the same principle as chlorine, however, as opposed to chlorine, chlorine dioxide has no harmful effects on human health.

Hypochlorite disinfection:-

Hypochlorite is applied in the same way as chlorine dioxide and chlorine. Hypo chlorination is a disinfection method that is not used widely anymore, since an environmental agency proved that the Hypochlorite for disinfection in water was the cause of bromated consistence in water.

Ozonation:

Ozone purifies air/water by disinfection, killing bacteria, viruses and odour. Ozone will inhibit corrosion, scaling, fouling and slime leading to increased efficiency and overall longer life of the tower Waste water blow down will reduce substantially and will help the user in complying with environmental regulations before discharging out Ozone prevents the growth of bio-organisms such as algae Bacterial build-up and threat of human infection are reduced considerably with Ozone

Ozone disinfection:-

Ozone is a very strong oxidation medium, with a remarkably short life span. It consists of oxygen molecules with an extra O-atom, to form O₃. When ozone comes in contact with odour, bacteria or viruses the extra O-atom breaks them down directly, by means of oxidation. The third O-atom of the ozone molecules is than lost and only oxygen will remain.

Disinfectants can be used in various industries. Ozone is used in the pharmaceutical industry, for drinking water preparation, for treatment of process water, for preparation of ultra-pure water and for surface disinfection.

Chlorine dioxide is used primarily for drinking water preparation and disinfection of piping.

Every disinfection technique has its specific advantages and its own application area. In the table below some of the advantages and disadvantages are shown:

Technology	Environmentally friendly	Byproducts	Effectivity	Investment	Operational costs	Fluids	Surfaces
Ozone	+	+	++	–	+	++	++
UV	++	++	+	+/-	++	+	++
Chlorine dioxide	+/-	+/-	++	++	+	++	—
Chlorine gas	—	—	–	+	++	+/-	—
Hypochlorite	—	—	–	+	++	+/-	—

Neutralizing agents (alkalinity control):-

In order to neutralize acids to bases, we use sodium hydroxide solution (NaOH), calcium carbonate, or lime suspension (Ca (OH) ₂) to increase pH levels. We use diluted sulphuric acid (H₂SO₄) or diluted hydrochloric acid (HCl) to decline pH levels. The dose of neutralizing agents depends upon the pH of the water in a reaction basin. Neutralization reactions cause a rise in temperature.

Oxidants

Chemical oxidation processes use (chemical) oxidants to reduce COD/BOD levels, and to remove both organic and oxidizable inorganic components. The processes can completely oxidize organic materials to carbon dioxide and water; although it is often not necessary to operate the processes to this level of treatment a wide variety of oxidation chemicals are available. Examples are:

• Hydrogen peroxide
• Ozone
• Combined ozone
• Peroxide
• Oxygen

Hydrogen peroxide:-

Hydrogen peroxide is widely used thanks to its properties; it is a safe, effective, powerful and versatile oxidant. The main applications of H₂O₂ are oxidation to aid odour control and corrosion control, organic oxidation, metal oxidation and toxicity oxidation. The most difficult pollutants to oxidize may require H₂O₂ to be activated with catalysts such as iron, copper, manganese or other transition metal compounds.

Ozone:-

Ozone cannot only be applied as a disinfectant; it can also aid the removal of contaminants from water by means of oxidation. Ozone then purifies water by breaking up organic contaminants and converting inorganic contaminants to an insoluble form that can then be filtered out. The Ozone system can remove up to twenty-five contaminants.

Chemicals that can be oxidized with ozone are:
· Absorbable organic halogens;
· Nitrite;
· Iron;
· Manganese;
· Cyanide;
· Pesticides;
· Nitrogen oxides;
· Odorous substances;
· Chlorinated hydrocarbons;
· PCB’s.
Oxygen:-

Oxygen can also be applied as an oxidant, for instance to realize the oxidation of iron and manganese. The reactions that occur during oxidation by oxygen are usually quite similar.
These are the reactions of the oxidation of iron and manganese with oxygen:

2 Fe²⁺ + O₂ + 2 OH^– -> Fe₂O₃ + H₂O
2 Mn²⁺ + O₂ + 4 OH^– -> 2 MnO₂ + 2 H₂O

Oxygen scavengers:-

Oxygen scavenging means preventing oxygen from introducing oxidation reactions. Most of the naturally occurring organics have a slightly negative charge. Due to that they can absorb oxygen molecules, because these carry a slightly positive charge, to prevent oxidation reactions from taking place in water and other liquids.

Oxygen scavengers include both volatile products, such as hydrazine (N₂H₄) or other organic products like carbohydrazine, hydroquinone, diethylhydroxyethanol, methyl ethyl ketoxime, but also non-volatile salts, such as sodium sulphite (Na₂SO₃) and other inorganic compounds, or derivatives thereof. The salts often contain catalyzing compounds to increase the rate of reaction with dissolved oxygen, for instance cobalt chloride.

pH Conditioners:- 

Municipal water is often pH-adjusted, in order to prevent corrosion from pipes and to prevent dissolution of lead into water supplies. During water treatment pH adjustments may also be required. The pH is brought up or down through addition of bases or acids. An example of lowering the pH is the addition of hydrogen chloride, in case of a basic liquid. An example of bringing up the pH is the addition of Natrium hydroxide, in case of an acidic liquid. The pH will be converted to approximately seven to seven and a half, after addition of certain concentrations of acids or bases. The concentration of the substance and the kind of substance that is added, depend upon the necessary decrease or increase of the pH.