FACULTY OF ENGINEERINGDEPARTMENT OF CHEMICAL & PROCESS

ENGINEERINGWASTEWATER TREATMENT

The Objective of this lecture is to:

Enable students understand the anaerobic treatment principal

Enable students understand the guidelines for an Agro – Processing Engineer during the Design, supervision and operation of anaerobic reactors being used in most food industries today.

Presentation Outline Overview of Cleaner production in SCOUL Waste water Parameters and functions to be considered by

an Agro – Processing Engineer during the Design of a wastewater treatment facility.

Basic information on anaerobic treatment of wastewater Details of SCOUL Anaerobic wastewater treatment process Operational techniques for process control and maintenance

of waste water treatment facility Laboratory Analysis of wastewater Waste management in SCOUL CO2 Plant

Sugar Corporation of Uganda Ltd (SCOUL) practices the Proactive type of Cleaner production. This involves the following:

Good housekeeping, Input substitution, Better process control, Equipment modification, Technology change, Product modification, efficient use of energy resources and On-site recovery/reuse

Overview of Cleaner production in SCOUL

What are the waste water Parameters and functions to be considered by an Agro – Processing Engineer during the Design of waste water treatment facility?

Waste water Parameters TSS COD

BOD5

PH Alkalinity Volatile Acids Nitrogen/Phosphorous

Physical properties Density Viscosity Surface Tension Osmotic Pressure Electrical Properties Optical Properties Functions Production Collection Storage Transfer Treatment Utilization

SCOUL ETP PLANT STANDARDS   RAW SPENT WASH DIGESTER OVERFLOW

PH 3.5 – 4.0 7.4 – 7.6 7.6 – 7.8Temp >35 36 - 38⁰C 38⁰CVolatile Acids - <3000 - Alkalinity - >6000 - COD 120000 - 130000 35000 - 40000 <35000TSS 8000 - 5000COD Reduction ≈ 70% (Minimum)

PRESSURE TO DIGESTER WHILE GAS TO FLARE STACK 150 – 250 mmwc

PRESSURE IN DIGESTER WHILE GAS TO GAS HOLDER 100 mmwcRECIRCULATION AT LAMELLA CLARIFER ≤ 50% OF THE FEED 

FLOW

SCOUL ETP Process Overview The influent wastewater is taken from the buffer tank. The liquid

flow is measured by a flow meter installed on the rising main. The MS fabricated tank is rested on a suitable foundation. Specially

designed Top & Side Entry mixing arrangement helps to keep reactor contents in constant suspension.

The influent waste water enters the central well of the digester. The flow of the wastewater is from top to bottom to maximize travel path and more contact time. This also ensures the proper distribution of bacterial population throughout the reactor and avoidance of low pH zones within it

Cont. SCOUL ETP Process Overview

The microbes in suspension metabolize the organic matter present in wastewater. Both acidification and methanisation takes place simultaneously in the reactor. The semi-continuous/continuous mixing aids better contact and higher reduction of organic matter.

The mixed liquor leaves the digester from top overflow arrangement. It then enters Degasser, wherein, the dissolved gases are released to atmosphere.

The out flow from the degasser then enters Lamella settler. The settled sludge from lamella is recycled back to compartments as per requirement. The overflow of lamella is taken to the subsequent treatment units of SCOUL Bio compost facility

The biogas generated by anaerobic process bubbles up to the top of reactor & is then conveyed to Gas Holder

WHAT ARE THE MAIN AD PROCESSES?

Hydrolysis. The waste materials of plant and animal origins consist mainly of carbohydrates, lipids, proteins and inorganic materials. Large molecular complex substances are solubilized into simpler ones with the help of extra cellular enzyme released by the bacteria.

Acidification: The monomer such as glucose which is produced in Stage 1 is fermented under anaerobic condition into various acids with the help of enzymes produced by the acid forming bacteria. The volatile acid content of the anaerobic reactor usually runs in the range of about 1000mg/L to 3500mg/L expressed as acetic acid

Methanisation: The principle acids produced in Stage 2 are processed by methanogenic bacteria to produce methane. which use the volatile acids produced by the acid former as food. The acids are then converted to methane and carbon dioxide gases as major end products . EQUATONS

PRODUCTS OF ANAEROBIC DIGESTION

1. GasesThe major gases produced in anaerobic

digestion are methane and carbon dioxide. These gases are collected and compressed. This methane rich gas is used as a fuel gas for SCOUL Distillery boiler.

Analyzing gas purity

PRODUCTS OF ANAEROBIC DIGESTION

2. Treated wastewater

The organic matter of the wastewater is partially destroyed by the acidity bacteria and methane forming bacteria and the treated wastewater leaves the reactor with much reduced pollution potential

Analyzing pH of treated wastewater

ENVIROMENTAL FACTORS CONTROLLING DIGETION

Optimum Conditions for Anaerobic Treatment1. Oxygen or Air: Nil2. Temperature: 38°C – 42°C3. PH: 6.9 – 7.64. Toxic Materials: Nil

5. Volatile Acids: 1500<X<3000mgO2/L

6. Alkalinity: >6000

SAMPLING POINTS Influent: By analyzing this sample for pH, COD, BOD, the operator can decide on feeding

rate and predict to some degree how the reactor will perform.

Reactor Contents (Composite of diametrically opposite locations): This sample represents a well-mixed active portion of the reactor and gives the operator information on alkalinity and volatile acids as well as on the toxic materials

Treated Effluent: This sample should be taken from the overflow of lamella clarifier. This gives the exact idea of treatment efficiency of the whole anaerobic process. COD/BOD removal efficiency can be calculated based on the results of this sample.

d) Biogas: The biogas mainly comprises of CH4, CO2 and H2S. On routine basis, assuming that the CO2 and H2S are estimated by the Orsat apparatus and Tutwellers’ apparatus respectively and total contents of these two gases when subtracted from 100, would give percent methane content on volumetric basis.

LABORATORY ANALYSIS OF WASTEWATER

COD

Apparatus1) Reflux/Hot plate2) Condensers3) Reflux Flasks4) Analytical Balance5) Burette6) Pipette7) Conical Flasks

Reagents

1) Standard Potassium Dichromate (0.25N)

2) Sulphuric Acid reagent3) Ferroin indicator4) FAS5) Mercuric Sulphate, HgSO4,

Powder

Cont. of CODRefluxing Titrating against FAS

LABORATORY ANALYSIS OF WASTEWATER

Total Suspended Solids

Apparatus1) Centrifuge2) Test tubes3) Vacuum Oven4) Measuring Cylinder5) Analytical BalanceMaterials1) Distilled water2) Samples

Lab Centrifuge

Cont. of TSS

BIOCHEMICAL OXYGEN DEMAND

Apparatus

1) BOD bottles, 300ml2) An incubator3) DO meterReagents

1) Phosphate buffer solution2) Magnesium Sulphate solution3) Calcium chloride solution4) Ferric chloride solution5) Ferric chloride solution6) Acid and alkali solution. 1N NaOH and

1NH2SO47) Sample dilution water

LABORATORY ANALYSIS OF WASTEWATER

Vacuum Oven Reflux

WASTE MANAGEMENT IN CO2 CHEMICAL RECOVERY PLANT

SCOUL

Process Overview

FOAM TRAP – removes occasional foam carryover from fermentation.

BOOSTER COMPRESSOR – maintains fermenter pressure and provides pressure for purification and compression.

SCRUBBER – provides bulk removal of water-soluble impurities (such as alcohol) using potable water as the scrubbing liquid (minimal water consumption).

CO2 COMPRESSOR – elevates the CO2 gas pressure to allow for efficient purification, dehydration and liquefaction.

Cont. Process Overview AFTERCOOLER/PRECOOLER – reduces the gas temperature to

condense and remove water contained in the gas. This maximizes downstream equipment performance and efficiency.

DUAL TOWER DEODORIZER – removes impurities such as organic and sulfur compounds.

DUAL TOWER DEODORIZER/DRYER – From the main purification train CO2 vapor flows to two absorption driers. The driers contain silica gel, which removes almost all moisture from the CO2vapour. Silica gel is regenerated for four to six months before being removed and replaced

Cont. Process Overview LIQUEFACTION/STRIPPING SYSTEM – converts the CO2 gas to a

liquid form by use of refrigeration (i.e.: R-404A, NH3, etc.). This allows for convenient storage of the CO2 product and provides for additional purification of the CO2 by the partial removal of non-condensable gases (i.e.: O2 and N2) via stripping. Stripping systems are designed to provide a guaranteed liquid CO2 purity with <5 ppmv O2. It can also allow for earlier collection from fermentation, which increases the quantity of CO2 recovered.

LIQUID CO2 STORAGE TANK – receives and stores the liquid CO2 for reuse or resale.

Waste management in CO2 Plant

General Waste

All general wastes (including solid wastes, paper and domestic scraps) are collected in a hopper for later removal to a licensed disposal facility.

Sewage

All sewage is stored in a concrete effluent pit near the western boundary of thesite. A licenced waste disposal contractor pumps out the pits periodically and transports the waste to

a licenced sewage treatment plant Chemical Wastes

Chemical wastes including spent silica gel, activated carbon and Puraspec are collected by a licenced waste disposal contractor for disposal off-site. Empty chemical drums are returned to the bunded workshop storage area for subsequent collection and disposal off-site

Gaseous Emissions

Venting of CO2vapour (including fugitive releases) and methane is required duringoperations. Air Liquide is currently aiming to reduce CO2losses from 25% to 20%

THANKS FOR LISTENING