Wastewater treatment plant Report, Assignments of Civil Engineering

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University of Wasit ﺟﺎﻣﻌﺔ واﺳﻂ College of Engineering ﻛﻠﯿﺔ اﻟﻬﻨﺪﺳﺔ Department of civil engineering ﻗﺴﻢ اﻟﻬﻨﺪﺳﺔ اﻟﻤﺪﻧﯿﺔ

Report on (Wastewater treatment plant ( Grit

chamber , Primary sedimentation tank, Biological

treatment)

Made By :

Ali Hamid Kadhim

Supervised By Asst.Prof. Ali Jwaid

Table of Contents

WASTEWATER TREATMENT Page 1-INTRODUCTION - WHAT IS WASTEWATER AND WHAT IS IT MADE UP OF? 3 2-WHY IS IT NECESSARY TO TREAT HUMAN WASTE OR EXCRETA 3 3-DECIDING WHICH TREATMENT OPTION TO USE 4 4-WHAT IS WASTEWATER TREATMENT 4 5- LEVELS OF WASTEWATER TREATMENT 5 6-SEPARATION OF SOLIDS 7 7-WHAT ARE AEROBIC AND ANAEROBIC PROCESSES 8 8-SLUDGE ACCUMULATION 9 9-ELIMINATION OF NITROGEN 9 10-ELIMINATION OF PHOSPHORUS 9 11-ELIMINATION OF TOXIC SUBSTANCES 10 12-REMOVAL OF PATHOGENS 10 13-CALCULATIONS 11 14-CONCLUSION 14

1- Introduction - what is wastewater and what is it made up of? Human waste or more technically referred to as ‘excreta’ is defined by Chamber’s Concise 20th Century Dictionary as “useless matter discharged by animal alimentary”, animals being humans in this context. Excreta is made up of a solid matter, faeces, and a liquid matter, urine and is essentially an organic compound. The constituents making up the compound are carbon, nitrogen, phosphorous, sulphur and hydrogen. Also present are fats, carbohydrates, enzymes, proteins, trace elements, pathogens and many different bacteria. 2- Why is it necessary to treat human waste or excreta? It is necessary to treat human waste or excreta for many reasons, but the most important reason is to preserve health. Untreated human excrement contains a variety of pathogenic organisms, which include protozoa, bacteria, viruses and eggs of helminths that are disease-causing organisms. The presence of these in the environment transmits various types of diseases. They could be:

• Water borne where pathogens are present in water supplies
• Soil–based where the excreted organism is spread through the soil
• Insect-vector borne where the pathogen is spread by insects that feed or breed in water e.g. flies and mosquitoes.
• Faecal-oral transmission routes by which pathogens from faeces reach the mouth by either hand, clothes food etc.

3- Deciding which treatment option to use. Once excrements have been produced, it is necessary to decide what to do with the waste and determine the wastewater treatment option. There is a general distinction : Waste being treated on-site via various treatment options e.g. VIP latrines, water seal toilets, composting toilets etc. or by the use of water to carry the waste off-site to be treated some place else either not too far from the compound as with septic tanks or to specialised treatment plants through sewer lines. This form of waste often is referred to as wastewater or sewerage. The total management of wastewater can be separated into four categories:

• wastewater collection,
• wastewater treatment,
• treated wastewater disposal and,
• sludge management. Waste only becomes non-hazardous to human health after treatment 4- What is Wastewater Treatment? “The term treatment means separation of solids and stabilisation of pollutants. In turn stabilisation means the degradation of organic matter until the point at which chemical or biological reactions stop. Treatment can also mean the removal of toxic or otherwise dangerous substances (for e.g. heavy metals or phosphorous) which are likely to distort sustainable biological cycles, even after stabilisation of the organic matter.”(Sasse, 1998) General Parameters to measure organic pollution. COD (Chemical Oxygen Demand) is said to be the most general parameter to measure organic pollution. COD describes how much oxygen is required to oxidise

all organic and inorganic matter found in the wastewater sample. BOD (Biological Oxygen Demand) describes what can be oxidised biologically, with the help of bacteria and is always a fraction of COD. Usually BOD is measured as BOD meaning that it describes the amount of oxygen consumed over a five-day measurement period. It is a direct measurement of the amount of oxygen consumed by organisms removing the organic matter in the waste. SS (Suspended Solids) describes how much of the organic or inorganic matter is not dissolved in water and contains settleable solids that sink to the bottom in a short time and non-settleable suspended solids. It is an important parameter because SS causes turbidity in the water causing clogging of filters etc. The mentioned parameters are measured in 'mg/l'. 5- Levels of Wastewater Treatment Wastewater treatment options may be classified into groups of processes according to the function they perform and their complexity: Preliminary Treatment – includes simple processes that deal with debris and solid material. The purpose of preliminary treatment is to remove those easily separable components. This is usually performed by screening (usually by bar screens) and grit removal. Their removal is important in order to increase the effectiveness of the later treatment processes and prevent damages to the pipes, pumps and fittings. Primary Treatment – is mainly the removal of solids by settlement. Simple settlement of the solid material in sewage can reduce the polluting load by significant amounts. It can reduce BOD by up to 40%. Some examples of primary treatment are septic tanks, septic tanks with upflow filters, Imhoff tanks.

Secondary Treatment – In secondary treatment the organic material that remains in the wastewater is reduced biologically. Secondary treatment actually involves harnessing and accelerating the natural process of waste disposal whereby bacteria convert organic matter to stable forms. Both aerobic and anaerobic processes are employed in secondary treatment. Some examples of secondary treatment are UASB, reed bed systems, trickling filters and stabilisation ponds. Tertiary treatment – is the polishing process whereby treated effluent is further purified to acceptable levels for discharge. It is usually for the removal of specific pollutants e.g. nitrogen or phosphorus or specific industrial pollutants. Tertiary treatment processes are generally specialised processes. Some examples of tertiary treatment are bank’s clarifiers, grass plots, etc. Small Scale Wastewater Treatment Project, Phase 1 Page 10 [TR288 – Schölzel & Bower] The majority of secondary treatment processes are biological in their nature – i.e. they use the natural activity of the bacteria to break down polluting material. Biological treatment processes can themselves be divided into two general sub-divisions – aerobic and anaerobic processes. Advanced or quartiairy treatments are applicable only to industrial wastes to remove specific contaminants. Figure 3 gives an overview on technologies and their categorisation

1-Primary treatment :Bar or Bow Screen Grit removal Sedimentation Oil/ fat removal Flow equalisation pH neutralisation Imhoff tank 2-Secondary Treatmen t:Activated Sludge Extended aeration Aerated lagoon Trickling filter Rotation bio-discs anaerobic Sequence batch reactor Anaerobic filter 3-Tertiary Treatment :Nitrification Denitrification Chem. Precipitation Disinfection Filtration Chemical oxidation Biological P removal 4-Advanced Treatment :Chemical treatment reverse Osmosis Electrodialysis Carbon adsorption Selective ion exchange Hyperfiltration ‘Treatment categorisation and technologies, Source: Veenstra and Alaerts (1996)’ 6- Separation of solids Wastewater treatment also relies on the separation of solids, both before and after stabilisation. The choice of method of solid removal will depend on the size and specific weight of pieces and particles of suspended solids. Screening For the larger pieces of solids for e.g. diapers, cloth, etc. in wastewater treatment. Screens require cleaning at very short intervals. Materials captured through screening require a safe place to be disposed of. Below is a diagram of waste stabilisation ponds showing screening as the first stage. Sedimentation Separation of solids happens primarily by gravity, predominantly through sedimentation. Coarse and heavy particles settle within a few hours or minutes while smaller and lighter particles may need days and weeks to sink to the bottom.

Flotation Flotation is the predominant method to remove fat, grease and oil. Unwanted flotation occurs in septic tanks and other anaerobic systems where floating layers of scum are easily formed. Accumulated scum could be removed manually or left purposely to seal the surface of anaerobic ponds to prevent bad odour. Below is a diagram of a septic tank showing scum floating on the surface. 7- What are aerobic and anaerobic processes? With aerobic processes, bacteria use oxygen to feed on the organic material (which is a food source) to produce carbon dioxide and water, with the production of quantities of extra bacterial mass (sludge). Most aerobic processes require the mechanical addition of oxygen and that can be expensive. Anaerobic processes take place in the absence of oxygen and bacteria break down the organic wastes to produce carbon dioxide and methane. This mixture of gases, called Biogas, can potentially be harnessed as an energy source. Anaerobic processes produce much less excess sludge than aerobic processes however the treatment efficiency is not as high as it is for aerobic processes. The aerobic process happens much faster than anaerobic digestion and for that reason always dominates when free oxygen is available. The high speed at which decomposition occurs is caused by the shorter reproduction cycles of aerobic bacteria as compared to anaerobic bacteria. Anaerobic bacteria leave some of the energy unused and it is this unused energy which is released in the form of biogas. Aerobic bacteria use a larger portion of the pollution load for production of their own bacterial mass compared to anaerobic bacteria, which is why the aerobic process produces twice as much sludge as the anaerobic process. Aerobic treatment is highly efficient when there is enough oxygen available.

8- Sludge accumulation Sedimentation and particles that escape filtration lead to sludge accumulation at the bottom of vessels. This sludge gets compacted over time, consequently older sludge occupies less volume than fresh sludge. Sludge removal is important and removal should be performed as specified for each technology. 9- Elimination of Nitrogen Nitrogen is a nutrient that causes algal growth in receiving waters and needs to be removed from wastewater before discharge. It is also poisonous to fish in the form of ammonia gases and also may become poisonous in the form of nitrite. The basic process of nitrogen removal occurs in two steps, namely, nitrification (aerobic conditions) followed by denitrification (anaerobic conditions) with the result that pure nitrogen diffuses into the atmosphere. Nitrate is the most stable form of nitrogen and its’ presence indicates complete oxidation 10- Elimination of Phosphorus Phosphorus is a nutrient that is water soluble, often recycled and is required to support living plants and organisms. Bacteria cannot transform phosphorus into a form in which it loses its fertiliser quality permanently. This implies that no appropriate biological process either aerobic or anaerobic can remove phosphorous from wastewater. Phosphorus removal from water normally takes place by removal of bacterial mass (active sludge) or by removal of phosphate fixing solids via sedimentation or flocculation. This process is normally performed in the tertiary stage of treatment.

11- Elimination of toxic substances Most heavy metals are toxic or carcinogenic and therefore should not remain in the wastewater because they harm the aquatic life of the receiving water or could enter the human nutritious cycle when wastewater or sludge is used in agriculture. Since heavy metals settle easy their removal is not difficult however soluble toxic substances may be difficult to remove. There are numerous methods for converting toxins into non-toxic substances for e.g. ion exchange procedures. 12- Removal of pathogens Pathogens are present in many forms in excreta e.g. bacteria, viruses and protozoa and accumulate in the sediment sludge and are largely retained inside the treatment system where they stay alive for several weeks. Most bacteria and viruses caught in the sludge die after shorter periods. Those bacteria, which are not caught in the sludge but remain suspended in the liquid portion, are hardly affected, meaning, these bacteria and viruses exit the plant fully alive. Exposure to UV rays has a substantial hygienic effect. High pathogen removal can also be experienced in shallow ponds with long retention times. Constructed wetlands with their multifunctional bacterial life in the root zones can also be very effective. Using chlorination to kill pathogens is only advisable for hospitals in the case of epidemics and other such special circumstances as chlorine kills all forms of bacteria both beneficial and non-beneficial. Apart from this chlorine has an adverse impact on the environment. Water is made unstable as chlorine itself has a high chemical oxygen demand (COD).

13- Calculations Design a grit chamber and primary sedimentation tanks for wastewater treatment plant served population 1250000 capita and q= 300liters / capita .day , if BOD inlet = 400 mg/l and SS inlet 400 mg/l. SOL// DWF = Qave = Nq = 1250000300 = 375000 m3/day 3WF = 3* 375000 = 1125000 = 781.25 m3/min Use t = 2min, (2-5) min. Volume V = 781.25*2= 1,562.5 m Using at least two tanks = V = = 781.25 m 2

Let the depth of the tank H = 4m and L = 3w Area = Volume/Depth = 781.25 / 4 = 195.3 m Area = WL ⇒ 195.3 = 3 W^2 ⇒ W = 8m L = 3 W ⇒ 38 = 24 m Dimension of the chamber ( LWH) = 248 Checking dimension time ( should be between 2-5 min.) T = V/Q = = 2 minutes OK. 2

24 8 4* *

Designing of power supply (Blower)

Qair = (0.3 − 0.7) = 0.5 * 24 = 12 m3/ min

m 3 min − m length

P = [( ) -1 ]

8.41 (^) * E M (^) * R T * P 1 P (^2) γ γ− Air density = 1.2 kg/m Mass = density × volume Mass = ρ × volume Mass = ρ × Q × t = 1.2 * 12 * 1min/60 sec = 0.24 Kg/sec T = 273 + 30 = 303 K

P = [( ) -1 ]

8.41 0.7* 0.24 8.314 303* * 1 1.3 (0.2857) = 7.99 Kwatt ≃ 8 Kwatt Use 2 × 8 = 16 Kwatt

Primary Sedimentation tank

Designing of Primary Sedimentation Tank

DWF = Qave = N × q = 1250000*300 = 375000 m3/day Use 4 sedimentation tanks ⇒ Q = 375000 / 4 = 93750 m3/day Assume surface overflow rate SOR = 40 m/day SOR = Q / A ⇒ A = Q / SOR = 93750 / 40 = 2343.75 m

Area = *D ⇒ 2343.75 = *D ⇒ D = 54.6 m 55 m

4 Π 2 4 Π 2 ≃

Area = *(55) = 2375.82 m

4 Π 2 Volume = Q × t = 9375024 *2 hrs. = 7812.5 m Depth H = Volume / Area = 7812.5 / 2375.82 = 3.3 m

Total depth = 3.3 + 0.5 = 3.8 Use H = 4 m Check SOR ⇒ SOR = Q /A = 93750 / 2375.82 = 39.46 mg/day OK (20-80)mg/day

Mass Balance

From Figures 23-1 and 23- We can find SS and BOD removals % SOR = 39. ∴ BOD removal = 36% and SS removal 57% For BOD Removal ∗ BOD input = 400 × 93750 = 0.4 * 93750 = 37,500 Kg/day ∗ BOD Removal = 0.36 × 37500 = 13500 Kg/day ∗ BOD output = 0.64 × 37500 = 24000 Kg/day For SS Removal ∗ SS input = 0.4 × 93750 = 37,500 Kg/day ∗ SS Removal = 0.57 ×37,500 = 21,375 Kg/day ∗ SS output = 0.43 × 37,500 = 16,125 Kg/day ∗ Assume percentage of Solids in Sludge = 5% ∗ Assume density of Sludge = 1017 Kg/day ∗ Mass of Solids = SS in sludge / SS % = 21,375 / 0.05 = 427, ∗ Q sludge = Mass of Sludge / ρ sludge = 427,500 / 1017 = 420.4 m3/day Concentration of BOD ∗ BOD input = 0.4 kg/m ∗ BOD Removal = 13500 / 420.4 = 32.11 Kg/m ∗ BOD output = = 0.257 Kg/day = 257 Kg/L 24000 93750 − 420.

Concentration of SS ∗ SS input = 0.4 Kg/m ∗ SS Removal = 21,375 / 420.4=50.84 Kg/m ∗ SS output = = 0.172 Kg/day =172 Kg/L 16, 93750 − 420. 14- Conclusion Wastewater treatment involves a variety of processes performed at different levels of treatment. The basic form of treatment is the breaking down of organic waste by bacteria either aerobically or anaerobically or a combination of both which occurs in secondary treatment. Primary treatment offers the settlement of solids. Tertiary treatment involves the removal of phosphorus, nitrogen and toxic substances. Pathogen removal occurs throughout treatment but becomes more effective mostly at tertiary levels through the use of UV rays and chlorination. The higher the treatment efficiency the better the quality of effluent produced.