Wastewater Treatment Explained PDF

Treatment of Wastewater © Innopharma  Treatment of Wastewater Created as a result of a process or as a result of a cleaning operation May contain a number of contaminants Condition of the IPC licence is that all waste waters are fully characterized...

Treatment of Wastewater © Innopharma  Treatment of Wastewater Created as a result of a process or as a result of a cleaning operation May contain a number of contaminants Condition of the IPC licence is that all waste waters are fully characterized All toxic chemical/contaminants are removed (or recycled and recovered) The wastewater treatment plant removes contaminants from wastewaters to produce a final effluent (output) So now safe disposal is possible! © Innopharma © Innopharma 73  Treatment of Wastewater The amount of treatment required depends on the water quality objectives of the receiving water supply. A typical treatment process may involve 3/4 stages: A combination of physical, chemical, and biological processes are used for wastewater treatment process. © Innopharma © Innopharma 75  Before discussing primary, secondary and tertiary processes, lets first discuss the physical and chemical methods of cleaning wastewater © Innopharma  Physical and Chemical Methods (wastewaters) Used to remove hazardous substances from the wastewaters. Part of the 3 stages of wastewater treatment. Substances can be removed from wastewaters by simple physical processes such as: © Innopharma  Physical Processes Sedimentation & Clarification Removal of suspended solids from liquids by gravity settling. © Innopharma  Physical and Process Filtration Involves the passing of wastewater through a filter medium (HEPA filter) which retains the solids and the liquid passes through © Innopharma  Physical and Process Filtration Sand filters used as a final polishing step in treatment of wastewater. This gives very clear effluent. Various types of filters from simple sand filters to rotary drum vacuum filters, belt presses, and filter presses. Filter presses are commonly used to de-water sludge’s This produces a solid waste which may need to be treated before release. © Innopharma  Physical and Process Centrifugation Involves subjecting wastewater to centrifugal force speed. Solids settle to the bottom. This process is often used for dewatering of waste sludge and produces a solid waste called a cake, which is then disposed of by incineration or landfill. Some chemicals (heavy metals) are toxic to humans and the environment & need to be removed from the wastewater before discharge. Also….. e.g. excess phosphates and nitrates result in rapid growth of algae, depletes oxygen, leads to fish kills. Low conc. of O2 is due to excess nutrients (eutrophication). © Innopharma  Physical and Process Centrifugation © Innopharma  Chemical Processes 1. Neutralisation Acid is added to alkaline waste or an alkaline added to an acid waste Result: Neutralise waste (i.e. pH of waste is adjusted to 6.5-8.0 Used as an early step in a waste treatment process Used so bacteria (in later stages of water treatment) stays alive So pH (acid/ alkaline) will not kill the population of bacteria needed to breakdown the organic park of the waste. © Innopharma © Innopharma 84  Chemical Processes 2. Oxidation The addition of strong oxidizing chemicals such as hydrogen peroxide (produces oxygen) Used to chemically breakdown organic wastes. © Innopharma  Chemical Processes 3. Precipitation Addition of specific chemicals to wastewater to cause fine solid materials to join together to form larger solids. Then separate by gravity These settle out of the liquid Chemicals referred to as: o Coagulant aids o Flocculation aids o Polyelectrolytes Choice depends on the nature of the material to be precipitated and the pH © Innopharma  Chemical Processes 4. Absorption Take in or soak up This is the addition of chemicals that absorb toxic organic chemicals Examples: Powdered charcoal absorbs a variety of toxic organic chemicals © Innopharma  Chemical Processes 4. Adsorption Adhesion to a surface to create a film on a surface Wastewater is filtered through an activated carbon filter. Activated carbon: Very effective for removal of dissolved organic chemicals Maximise effectives of the process, activated carbon adsorption is usually performed after secondary treatment. But, activated carbon media becomes exhausted and the filters need to be replaced, then incinerated. © Innopharma © Innopharma 89  Process/ Stages of Water Treatment © Innopharma  Process/ Stages of Water Treatment Wastewater treatment consists of separate treatment processes These are set up in series with the output (effluent) of one process becoming the input (influent) of the next process © Innopharma 14.7: Wastewater and Sewage Treatment - Chemistry LibreTexts © Innopharma 92 © Innopharma 93 © Innopharma  1. Pre-treatmemt/ Preliminary Treatment A physical process. Screening to remove large or hard solids, grit etc. This would block or damage equipment. Step typically includes grinders and bar screens (coarse and fine) to remove floating solids, paper and wood. Removed, bagged and treated as solid waste. © Innopharma © Innopharma 96 © Innopharma  The next stage is the Grit chamber Here, wastewater is held for a few minutes to allow sand, gravel and other heavy material to settle out. Material is collected and treated as solid waste. Result: The wastewater is sent for primary treatment. © Innopharma © Innopharma © Innopharma 100  2. Primary Treatment 1st stage of wastewater process After grit chamber, wastewater passes to a primary clarifier or a sedimentation tank and remains for at least 2 hours. The speed of flow is slowed to allow remaining suspended Sludge = Sludge is a by-product of the wastewater treatment process, solids, settle and form sludge at the bottom of the tank. consisting of organic and inorganic solids suspended in water. The sludge is then removed as a primary sludge. Floating solids e.g. grit, grease and scum. A physical process (sedimentation) that removes settle-able and floatable solids. © Innopharma  2. Primary Treatment Scrapers and skimmers are used to remove solids settled at the bottom and the scum at the top. Primary treatment reduces BOD by 30-40% and removes 40-70% suspended solids because most of the organic material is now removed. After primary treatment the wastewater goes for secondary treatment. © Innopharma 102 © Innopharma © Innopharma  3. Secondary Treatment 2nd Stage of wastewater process o A biological process involves microbes breaking down dissolved organic (biodegradable) waste. Removing BOD portion. o Speed up decomposition and utilize microbes which need organic matter (in the wastewater) to produce more microbes, water and CO2. o Two basic types of microbes: o Aerobic o Anaerobic © Innopharma © Innopharma 106  3. Secondary Treatment In Ireland, Activated Sludge System most commonly used. Wastewater treated with aerobic microbes (activated sludge) to breakdown the organic content of the waste. It consists of two parts: o Aeration Tank (“sludge” or mixed culture of microbes, which are constantly mixed and aerated) o Settling Tank or clarifier © Innopharma What is Activated Sludge? | Wastewater Digest  What is Aeration for Wastewater Treatment? | Wastewater Digest © Innopharma 108  Wastewater treatment facility providing secondary treatment using an activated sludge process © Innopharma  Wastewater enters the aeration tank and mixes with the sludge (containing bacteria) Microbes convert organic matter to more microbes plus CO2 (vented to the atmosphere) and water and reduce the BOD to acceptable levels. After 6-8hrs of agitation, wastewater flows into a secondary settling tank or clarifier. Here remaining solids (primarily microbes) settle out. The bacteria escape the microbes is returned back to the aeration tank (return activated sludge) to consume more organic material. The remainder of these solids are treated and disposed of as solid wastes The effluent from this stage undergoes the final stage of treatment. © Innopharma © Innopharma  4. Tertiary Treatment 3rd stage of wastewater process Physical and Biological processes to remove toxic compounds, bacteria and chemicals from secondary waste effluent. These remove the following: Responsible for residual BOD in secondary wastewater That may be hazardous or toxic Nutrients-nitrates and phosphates; hazardous toxic metals Disease causing microbes: bacteria, viruses, etc. © Innopharma  5. Disinfection The final process before effluent discharge. Allows destruction of harmful (pathogenic) microbes. Most commonly used: Chlorine in the form of liquified gas or sodium hypochlorite (BUT excess chlorine can be toxic to aquatic life) © Innopharma  5. Disinfection Following disinfection wastewater is now purified and can be discharged to the environment. Other disinfectants: Ozone; UV light UV Light to Disinfect Water © Innopharma © Innopharma 116 © Innopharma  6. Monitoring Continuous monitoring at all stages in treatment Tests: Requirement of the IPC licence and will ensure successful wastewater treatment © Innopharma  Treatment of Sludge © Innopharma  Treatment of Sludge Definition: Collection of solids removed at each stage of the wastewater treatment process e.g. during sedimentation, filtration, centrifugation processes. Sludge may require further processing to reduce the water content before final disposal (sludge dewatering) © Innopharma  Anaerobic Sludge Treatment A biological process (composting) that uses microbes that thrive in the absence of oxygen (an anerobic environment) Sludge or solid waste is fed to the digester under controlled conditions The tank is airtight (anaerobic) bacteria break down organic compounds The products are: o Biogases: Mainly of methane and CO2 o A digestate: Separated into a liquid and solid component © Innopharma Sludge Treatment - an overview | ScienceDirect Topics  Anaerobic Sludge Treatment Methane (a GHG) can be captured and used to produce heat or electricity. The liquid component (digestate) can be used as a fertilizer. The solid component may require further processing to reduce the water content before final disposal. Sludges can be treated by: o Dewatering o Thickening o Drying © Innopharma Sludge Treatment - an overview | ScienceDirect Topics  Filter Press for Dewatering © Innopharma  Conclusions Highly regulated process or processes are required to dispose of waste. There are a variety of methods available. Bacteria play a more significant role than you would expect. © Innopharma  Exam Prep Read the exam paper in full Read all questions carefully Answer only what was asked Answer all questions in your answer booklet Label your answers clearly Manage your time appropriately Question 1 and two other questions (Q2, Q3 or Q4) Don’t panic! © Innopharma  Suggested Exam Timings 2 Hour Exam (120 mins) 5-10 mins – Read the exam paper FULLY 30-33 mins – Per Question 5-10 mins – Read over your answers/ Fill in Cover Sheet © Innopharma  Suggested Exam Timings 2 Hour Exam (120 mins) 5-10 mins – Read the exam paper FULLY 30-33 mins – Per Question 5-10 mins – Read over your answers/ Fill in Cover Sheet Question 1 – Compulsory – ANSWER ALL (10 short questions) Answer any TWO of Q2, Q3, Q4 – Answer ALL parts © Innopharma  Topics Summary Lecture 1: H&S Legislation in Ireland - Safety, Health and Welfare at Work Act 2005 Safety Statements – Six Steps Work Permits Emergency Planning – Seven Step Evacuation Plan Health and Safety Authority (HSA) – Accidents/ Incidents Lecture 2: Chemical Safety in the workplace Classification of chemical hazards – Physio/ Health Effects/ Env. Carcinogens, mutagens, teratogens H & P Phrases/Statements* Chemical Labelling Safety Data Sheets (SDS) – 16 Sections Effects of Chemicals on the body – Exposure routes, Exposure Limits, LD50, Acute & chronic First Aid Treatment Noise – PPE, Exposure limit values, Exposure Action values Hazard Control – Hierarchy of Controls © Innopharma  Topics Summary Lecture 3: Biological hazards and safety in the workplace Sources of biological contamination Bacteria (spores), Viruses, Fungi (spores) Exposure routes Classification of biohazards – Group 1-4 & associated Biosafety level Control of Biohazards: Cleaning, Disinfection, Sterilisation Lecture 4: Sustainability Environmental Management – History (Brundtland Report, COP21, Seveso) Precautionary Principle, Polluter Pays Principle, Proximity Principle Responsible Care – Voluntary Code – Chemical Industry – 7 Codes/ Principles Waste Management Hierarchy Environmental Protection Agency (EPA) – IPC Licence Environmental Management Systems (EMS) © Innopharma  Topics Summary Lecture 5a & 5b: Waste – Hazardous and non-hazardous Waste Analysis – Chemical, Microbiological, Instrumentation Chemical: pH, BOD, COD, DO, Nutrient Analysis, Suspended Solids Gaseous Waste Treatment – Filtration, Scrubbing, Incineration Solid Waste Treatment – Chemical, Incineration, Landfill Wastewater Treatment – Primary, Secondary, Tertiary Sludge and Sludge Treatment © Innopharma