welcome you to todays webinar The Science Behind Wastewater - - PowerPoint PPT Presentation

The Welsh Area would like to welcome you to today’s webinar

The Science Behind Wastewater Treatment

Joshua Williams Process and Commissioning Scientist Welsh Water joshua.williams@dwrcymru.com

For membership information contact: Gemma.Williams@dwrcymru.com Record your CPD online by using the IW exclusive online portal. Go to ‘My Dashboard’ on your membership home screen and select ‘My CPD’ For sponsorship opportunities contact: Welsharea.instituteofwater@outlook.com

The ancient history of wastewater treatment

• Sanitation has played a pivotal part in human development, allowing for

rapid growth and improvements to life expectancy.

• Forms of wastewater management have existed since the start of human

development

• Some examples from our ancient history
• Domestic wastewater for irrigation – Bronze Age (ca. 3200-1100

BCE).

• The Mesopotamians introduced the world to clay sewer pipes

around 4000 BCE

• The ancient Greeks had a well-organized water system for taking
• ut waste water and storm sewage canals for overflow when there

was heavy rain.

• In medieval European cities, small natural waterways used for

carrying off wastewater were eventually covered over and functioned as sewers. The majority was discharged direct to watercourses.

The modern history of wastewater treatment

• The tremendous growth of cities during the Industrial Revolution quickly

led to terribly over polluted streets, which acted as a constant source for the outbreak of disease.

• As part of a trend of municipal sanitation programs in the late 19th and

20th centuries, many cities constructed extensive sewer systems to help control outbreaks of disease such as typhoid and cholera.

• Initially these systems discharged sewage directly to surface

waters without treatment. Later, cities attempted to treat the sewage before discharge in order to prevent water pollution and waterborne diseases.

• Early techniques involved land application of sewage on

agricultural land.

• In the late 19th century some cities began to add chemical

treatment and sedimentation systems to their sewers. Most cities in the Western world added more expensive systems for sewage treatment

• in the 20th century, after scientists at the University of

Manchester discovered the sewage treatment process

• f activated sludge in 1912.
• Some of the biggest developments took place in major cities

across the United Kingdom, this included Manchester, Liverpool and London.

The wastewater treatment process

• Before waste water can be treated it needs to be collected.

Every day in the UK over 624,200 kilometers of sewers collect

• ver 11 billion liters of wastewater from homes, municipal,

commercial and industrial premises and rainwater run-off from roads and other impermeable surfaces.

• The treatment provided at waste water treatment plants can

involve:

• Preliminary treatment – to remove grit and gravel and

screening of large solids.

• Primary treatment – to settle larger suspended, generally
• rganic, matter.
• Secondary treatment – to biologically break down and

reduce residual organic matter.

• Tertiary treatment – to address different pollutants using

different treatment processes.

• This is treated at about 9,000 sewage treatment works before

the treated effluent is discharged to inland waters, estuaries and the sea.

Primary Treatment

• Primary purpose of primary treatment is to reduce solids and
• rganic matter loadings.

Secondary Treatment – Biological Filters

• One of the earlier methods of treating sewage was to run it into

a tank filled with loose stone. These units were known as contact filters.

• A modification to convert them to continuous operation, rather

than batch, was made in 1893.

• Biological Principles
• This is an aerobic process
• Sewage is a suitable source of food for the micro-organisms in a

biological filter as it contains nitrogen, organic carbon compounds, phosphorus and trace elements.

• Air circulates in the voids between the media, taking oxygen to

the slime layer on the surface of the media.

• As sewage trickles over the media, the various organic

substances are absorbed onto the biological film thus supplying the organisms with food.

• If either food or oxygen is absent, this metabolism will stop.
• This process is most efficient when the slime layer is thin and

totally aerobic.

Secondary Treatment – Biological Filters

• The microorganisms absorb the organic matter in the

sewage and stabilize it by aerobic metabolism, thereby removing oxygen-demanding substances from the sewage. Trickling filters remove up to 85 percent of organic pollutant from sewage.

• Filters require the correct loading to operate efficiently this

is either achieved via the PSTs or in a side stream process for example a High Rate Filter (HRF)

• Overloading can result in poor Ammonia removal,
• Anaerobic decomposition, excess biomass
• Hydraulic loading also plays a major part in the health of a

biological filter

• Wetting rates – max 0.75 m3/m2/d.
• Sk factors – 5 mm/pass

Microorganisms

• Bacteria play the major part in the treatment process
• Nitrification takes place through the presence of Nitrifying

bacteria Nitrosomonas & Nitrobacter

• Typically these are too small to see under the microscope so a

range of other microorganisms are used to determine the health and condition of the biomass

• Protozoa : Feed on biofilm bacteria and helps in

maintaining high decomposition rate, examples :

• Flagellates (e.g., Bodo, Monas)
• Ciliates (e.g., Vorticella)
• Amoeba (e.g., Amoeba, Arcella)
• Rotifers
• Macroinvertebrates :
• Diptera (Fly)
• Nematodes (hookworm, lungworm etc.)

Nitrosomonas Europaea Flagellates Ciliates (Vorticella) Rotifers Nematodes

Activated Sludge

• The activated sludge process is a method of treating sewage in an aerated

bacterial sludge. effluent by settlement.

• Most of the settled activated sludge is returned for re- use referred to as

returned activated sludge (RAS)

• The excess is discharged as surplus activated sludge. (SAS).
• Treatment is optimised by maintaining the correct food to mass ratio (F:M) and

dissolved oxygen.

• Microscopic analysis aids the ability to maintain a stable process
• Changes to protozoa populations can indicate issues such as
• Oxygen deficiency
• Shock loading
• Toxicity
• The objective is to achieve a ideal F:M ration and sludge age

Activated Sludge – Filamentous Bacteria

• Filamentous bacteria are present in some abundance in all

activated sludge and some aid the flock formation process

• Low dissolved oxygen (DO), nutrient deficiency, In

appropriate F/M, and septicity can cause a rapid growth in certain types of filamentous bacteria

• This can have detrimental effects on the treatment process

resulting in poor solids settlement

Ideal sludge: Balance between filaments and floc-forming

• rganisms.

Bulking: Excessive quantities of filamentous organisms

• bserved.

Weak flocs: Absence of filamentous organisms.

Humus/Final Settlement

• Same principle and primary settlement tank
• Retention time should be 2 hours
• Typically radial flow circular tanks
• Hydraulics important to aid settlement
• Humus sludge shall generally be returned to primary

settlement tanks for co-settlement

Chemical Phosphorus Removal

• The objective is to remove phosphorus from the final

effluent of treatment works to improve the water quality of rivers

• Chemical removal is the most common form of treatment

used in the industry, however biological treatment and solids removal technologies exist.

• The objective of chemical removal is to flocculate the

phosphorus from the soluble form to a solid form using a metal salt.

• The solids are settled out using a sites primary settlement

tanks or humus settlement tanks and processed as part of the sludge stream

• The most common metal salts are Iron and Aluminum

based

• The main issues are around alkalinity effects and the

non selective nature of these chemicals

Chemical addition

Chemical Phosphorus Removal

• Molar ratios vary depending on target results and a

number of factors that can influence them are;

• pH
• Mixing method
• Wastewater characteristics
• Colloids and solids effect P-metal hydroxide

complexations

• Organic substrates
• Iron and aluminum can react with humic substances
• The correct dose rates to achieve this are done on a site to

site basis with sampling and jar test results (examples shown later)

Emerging Technologies

• In recent years a lot of focus has switched to several

emerging pollutants

• These include pharmaceuticals and more recently

microplastics

• As the industry comes to terms with the possibility of having

to treat these in the future, research and development is underway to review how we can meet them.

• However although the basics have worked well for 100s of

years, research continues everyday to look at different more energy efficient ways of treating wastewater

• A few examples we will look at today are;
• Membrane Biofilm Reactor (MBfR)
• Nanoparticle Treatment
• Passive aeration

Membrane Biofilm Reactor (MBfR)

• Use of hollow membrane fibers to deliver gas

(oxygen or hydrogen) to a surface biofilm for efficient removal of pollutant compounds (either reduced or oxidized).

• Oxygen- or air-based reactors have successfully

conducted concurrent nitrification and denitrification, high strength chemical demand

• xidation, and decomposition of

pharmaceuticals (Brindle et al. 1999; Downing and Nerenberg 2008)

• Hydrogen-based reactors safely treat oxidized

contaminants including nitrate, perchlorate, bromate, selenate, and chlorinated solvents such as trichloroethylene.

Nanoparticle Treatment

• Numerous studies have shown that

nanomaterials can effectively remove various pollutants in water and thus have been successfully applied in water and wastewater treatment.

• The most extensively studied nanomaterials;
• Zero-valent metal nanoparticles (Ag, Fe,

and Zn)

• Metal oxide nanoparticles (TiO2, ZnO, and

iron oxides)

• Carbon nanotubes (CNTs)
• Nanocomposites

Carbon nanotubes (CNTs)

• Carbon nanomaterials (CNMs) are a class of fascinating materials

due to their unique structures and electronic properties which make them attractive for fundamental studies as well as diverse applications, especially in sorption processes.

• Their advantages for water and wastewater treatment are;
• Great capacity to adsorb a wide range of contaminants,
• Fast kinetics
• Large specific surface area
• Selectivity towards aromatics
• Technology is emerging research so application may not be on

conventional WwTW but tailored more to effluent re-use

Passive Aeration

• A new energy-efficient process developed at

Murdoch University.

• Objectives are to achieve at least a 50 % energy

reduction compared to conventional solutions.

• 60-65% of energy consumption in activated

sludge plants is down to aeration

• Research aim to determine a more efficient way of

delivering oxygen to the water-dwelling bacteria than sending air bubbles to them through the wastewater.

The next 100 years

• The current demands from a rapidly growing

human population and the need for a more sustainable society are pushing forward new developments for sewage handling. These developments have two main drivers:

• General process improvements
• The contribution to the recycling of

resources.

• Innovation
• Energy reduced process
• Chemical free or alternative chemicals?
• Climate change.

The Role of a Process Scientist

• Primarily a process scientist is to offer support and

investigate issues on sites that are escalated via operations.

• However every day can vary from site based investigations,

to working with alliance partners on new schemes, innovation trial, trade effluent, pollution and so on….

• This can involve a multitude of activities
• Sampling, lab work, microscopic analysis
• Jar tests
• Process calculations
• Root cause analysis
• Regulator discussions
• Design and commissioning of schemes

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