Wastewater Content Flashcards

Question

Residential wastewater flow as a ratio to the average.

Answer 1

Maximum daily 2.25:1 Maximum hourly 3:1 Minimum daily 0.67:1 Minimum hourly 0.33:1

Answer 2

> 0.75 m/s.

Answer 3

Peak hourly flowrate = Average flowrate * Peaking factor (Use Chart)

Answer 4

the hydraulic conveyance system and other facilities such as sedimentation tanks and chlorine contact tanks where little volume is available for flow dampening.

Answer 5

A sewer is an artificial conduit (or pipe) or system of conduits used to remove sewage (human liquid waste) and to provide drainage.

Answer 6

C = R + V + B * O_t/O_s + S S_t/S_s C : Charge per unit of effluent R : reception and conveyance charge V : volumetric and primary treatment cost B : biological oxidation costs for settled effluent Ot : the effluent COD following one hour quiescent settling and with pH adjusted to 7.0 Os : the COD of the sewage S : treatment and disposal costs of primary sewage sludge St : TSS (total suspended solids) of the effluent Ss : TSS of the crude sewage

Answer 7

Biological oxygen demand Amount of O2 consumed by bacteria stabilising decomposable organic matter under aerobic conditions * Measures waste strength and treatment efficiency * Process is 95-99 % complete within 20 days (total or ultimate BOD) * 5 days BOD generally used (oxidation is 60 – 70% complete) * 20°C is used, average value for slow moving streams in temperate climates * Biochemical reaction rates are dependent on temperature

Answer 8

If sufficient oxygen is available  total decomposition of the biodegradable organic waste through 3 distinct activities: 1. Portion of the waste is oxidised to produce energy 2. Some of the energy is used to produce new cells 3. When all organic matter is used up, the new cells consume their own cell tissue

Answer 9

1. Oxidation COHNS + O2 + bacteria ==> CO2 + H2O NH3 + other products + energy 2. Synthesis COHNS + O2 + bacteria + energy ==> C5H7NO2 3. Endogenous respiration C5H7NO2 + 5O2 ==> 5CO2 + NH3 + 2H2O

Answer 10

The most widely used method is the 5 day BOD (BOD5). The sample is incubated at 20°C for five days. It is based on the measurement of dissolved oxygen involved in the biochemical oxidation of organic matter present in the water. 1. measure conc of DO in first sample 2. incubate 2nd sample in the dark at 20 degrees C for 5 days 3. measure the concentration of the DO in the second sample

Answer 11

BOD5 = (D1 - D2) / P D1: dissolved oxygen of diluted sample immediately after preparation, mg/L D2: dissolved oxygen of diluted sample after 5-day incubation at 20°C, mg/L P: fraction of wastewater sample volume to total combined volume, P = Vs/VB. VB: volume of the BOD bottle (usually VB = 300 mL) Vs: volume of the sample

Answer 12

BOD5 = ((D1- D2) - (B1 - B2)*f)/ P Vs: volume of the sample D1: dissolved oxygen of diluted sample immediately after preparation, mg/L D2: dissolved oxygen of diluted sample after 5-day incubation at 20oC, mg/L B1: dissolved oxygen of seed control before incubation, mg/L B2: dissolved oxygen of seed control after incubation, mg/L f: fraction of seeded dilution water volume in sample to volume of seeded dilution water in seed control, f = (VB-Vs)/VB P: fraction of wastewater sample volume to total combined volume, P = Vs/VB.

Answer 13

Amount of O2 consumed to chemically oxidise biodegradable and non-biodegradable organic matter under standard laboratory conditions

Answer 14

*Eutrophication is the enrichment of water with nutrients, usually phosphorous and nitrogen, which stimulates the growth of algal blooms and rooted aquatic vegetation. *Eutrophication promotes more plant growth and decay that in turn increases biochemical oxygen demand Algal blooms low levels of DO kills fish turbidity shifts in plants and animal population in surface water

Answer 15

*poorly replenished water bodies * natural lakes * artificial impoundment * bays * sluggish streams

Answer 16

Washing : to remove hazardous material for separate treatment Maceration: to facilitate compaction Dewatering : to reduce volume and weight Compaction: to reduce volume

Answer 17

Advantages : * Can be used for chemical addition, mixing, and flocculation ahead of primary treatment * Fresh wastewater, thus reduce odors and remove BOD5 * Minimal headloss * Grease removal by providing a skimming device * Remove some organic matter by air supply * Remove any desired size by controlling the air supply Disadvantages: * Volatile organic compound (VOC) and odor emission * Due to a health risk, covers may be required or nonaerated type grit chambers may be used. * High maintenance * High energy costs

Answer 18

*Widely used for selective removal of grits *Create a spiral current within the basin using diffused compressed air *Designed to remove grit particles having a specific gravity of 2.5 and retained over a 65-mesh (0.21-mm ) screen *Used for medium to large treatment plants

Answer 19

Grit: sand, dust, cinder, bone chips, coffee grounds, seeds, eggshells, and other materials in wastewater that are heavier than organic matter. Typical domestic sewage grit ranges from 105 to 300 um Reasons for grit removal *To protect moving mechanical equipment and pumps from unnecessary wear and abrasion *To prevent clogging in pipes, heavy deposits in channels *To prevent cementing effects on the bottom of sludge digesters and primary sedimentation tanks *To reduce accumulation of inert material in aeration basins and sludge digesters which would result in loss of usable volume

Answer 20

Sedimentation is the separation from water, by gravitational settling, of suspended particles that are heavier than water It is used for grit removal, particulate-matter removal in the primary settling basin, biological-floc removal in the activated-sludge settling basin, chemical floc removal. In most cases, the primary purpose of sedimentation is to produce clarified effluent but it is also necessary to produce sludge with solids cc that can be easily handled and treated. *Removal efficiency *BOD5: 30~40% *TSS: 50~70%

Answer 21

Free discrete settling (type 1) *Occurs in settling of a suspension of low solids concentration <500 mg/L. * Particles settle as individual entities, *No significant interaction with neighbouring particles * e.g. grit and sand particles from wastewater no interaction between particles as they settle

Answer 22

Flocculent settling (type 2) *Occurs in dilute suspension of particles that coalesce, or flocculate, *Particles coalesce or flocculate during settling so that their mass increases and settling velocity increases as they fall. *Occurs in primary and secondary sedimentation tank treatments. *Also occurs during removal of chemical flocs in settling tanks. Interaction between particles as they settle

Answer 23

Hindered settling (type 3) *Occurs in suspensions of intermediate concentration (500 to 2000 mg/L) *Interparticle forces hinder the settling of neighbouring particles. *The particles tend to remain in fixed positions with respect to each other, and the mass of particles settles as a unit. *A distinct “solid-liquid interface” develops at the top of the settling mass with clarified liquid above and particle mass below. *Occurs in secondary settling facilities used in conjunction with biological treatment facilities

Answer 24

Compression settling (type 4) *Occurs in solutions containing sufficiently concentrated particles that they form a structure (gel-like). *Settling occurs by compression of the structure (water gets squeezed out) by the weight of additional solids settling from above. *Usually occurs in the lower layers of a deep sludge mass (e.g. bottom of a deep secondary settling tanks; sludge thickening facilities).

Answer 25

aerobic (require oxygen for their metabolism, get their oxygen from air) anaerobic (grow in the absence of oxygen from air) (but when get it from sulphate (SO4 2- ), nitrate (NO3 -), carbonate (CO3 2+) and the like  anoxic conditions) facultative (can proliferate either in absence or presence of oxygen).

Answer 26

* The microorganisms are attached to a surface over which they grow (ex. rock, plastic, wood) * Recycling of settled biomass is not required

Answer 27

* The microorganisms are suspended in the WW * Recycling of settled biomass is required.

Answer 28

A measure of the character of organic matter i.e. how easily it is oxidised by microorganisms = BOD/COD * BOD biological oxygen demand (BOD5 = BOD over 5 days ) (the amount of oxygen used in bio oxidation) * COD chemical oxygen demand ( the amount of oxygen used in complete chemical oxidation)

Answer 29

*In a biological reactor the microorganisms are not generally dosed but are allowed to develop within the reactor and must be allowed to reach a sufficient concentration to deal with the amount of substrate to be removed. *At steady state, the concentration of biomass in the reactor is kept constant by removing an amount equivalent to the amount of substrate removed.

Answer 30

- Trickling filter - Rotating biological contactors

Answer 31

* Outer portion of biofilm is aerobic * If film gets too thick then inner portion can become anaerobic * When microorganisms near media surface die => lose ability to attach to surface and the biofilm de-attach: * New biofilm grows * Causes high BOD and SS if the effluent if not treated => add a sedimentation basin.

Answer 32

* Media on rotating shaft * Problem when shaft fails * Issue restarting after power failure * Usually applied to populations < 500

Answer 33

– Activated sludge process - most common secondary wastewater treatment process in use. – Aerated lagoons – Sequencing batch reactors (SBR) – Aerobic digesters (sludge treatment) – Membrane bio-reactors (MBR) *Suspension is achieved by mixing by mechanical stirrers or air bubbles *The same equipment provides air /oxygen for the reactions

Answer 34

Food to Mass ratio F/M * Is there enough biomass in the reactor to deal with all the carbonaceous matter coming in? * Is there enough carbonaceous matter coming in to provide food for the biomass and keep it growing? Sludge Age Average residence time of bacteria must be long enough to allow reproduction and not so long that a significant proportion is dying or dead Oxygen transfer rate – must be sufficient to meet the demands of the reactions (stoichiometry/efficiency) Typically uses lots of power

Answer 35

- Reliant on power for aeration and returning sludge (RAS) - Foaming (detergents, filaments) - Poor settlement

Answer 36

- fill, aerate, decant cycle in one tank - no or very little RAS

Answer 37

- Membrane instead of settlement to separate flocs from final effluent - No or little RAS

Answer 38

Biological nutrient removal BNR is a process used for nitrogen and phosphorus removal from wastewater using microorganisms before it is discharged into surface or ground water Aim is to remove nitrogen and phosphorus from wastewater – why? – ammonia affects fish; nitrate and phosphorus are nutrients which cause eutrophication in receiving waters (e.g. excess plant growth, low dissolved oxygen, murky water, depletion of desirable flora and fauna).

Answer 39

Constructed wetlands can be defined as engineered water saturated areas in which the natural removal processes for the water pollutants are reproduced and enhanced in order to optimise the purification performances.

Answer 40

-Secondary treatment of domestic or municipal wastewater industrial wastwater - tertiary treatment at polishing stage in conventional treatment plants - Diffuse pollution treatment : agricultural runoff, urban runoff, highway runoff etc... - Landfill leachate - Sludge dewatering and mineralisation

Answer 41

Constructed wetlands can be classified according to the life form of the macrophytes (aquatic plants growing in or near water ) in the system: 1. Floating : Macrophyte based system 2. Submerged : macrophyte based systems 3. Rooted emergent macrophyte - based system

Answer 42

Sub surface flow SSF Free water surface FWS

Answer 43

- Gravity settlement - Buoyancy flotation Air bubbles: Air bubbles are added or caused to form in one of the following methods: *Injection of air while the liquid is under pressure, followed by release of the pressure (dissolved-air flotation DAF) *Aeration at atmospheric pressure (air flotation) *Saturation with air at atmospheric pressure, followed by application of a vacuum to the liquid (vacuum flotation) *Decarbonation and electrolysis

Answer 44

Dissolved air flotation : Enhances floc separation rates by attaching floc particles to microscopic air bubbles

Answer 45

- Coloured waters - High TOC and Natural organic matter content - low to medium turbidity - High algae causing filter problems - High Fe and Mn seasonal content

Answer 46

*The purpose of coagulation/flocculation is to produce particles, by means of aggregation, that can be removed by inexpensive particle-separation procedures such as gravity sedimentation and filtration. *Aggregation of particulate material is a two-step process: coagulation followed by flocculation.

Answer 47

- Reduces the interparticulate forces by destabilising charged species - Extremely rapid process - Organic and inorganic coagulants can be used

Answer 48

-The size of particles increases as a result of particle collisions. (1) microflocculation (perikinetic flocculation), particle aggregation is due to thermal motion of fluid molecules - Brownian motion (2) macroflocculation (orthokinetic flocculation), particle aggregation is induced by velocity gradient and mixing. - Slow process - 20 to 40 minutes - Temperature sensitive - Flocculation aids (high molecular weight; low charge density; anionic, cationic,non-ionic) - Floc settling rate 0.1 to 3 m/h

Answer 49

*Redox (oxidation-reduction) reactions involve the transfer of electrons from one atom or ion or molecule to another atom or ion or molecule. *The driving force for the exchange of e- is a decrease in the electrical potential. *The addition of an oxidant to water involves a redox reaction when e- are transferred from the reductant to the oxidant.

Answer 50

removal or inactivation of pathogenic micro organisms Not the same as sterilisation - removal or inactivation of all micro organisms Usually the final barrier

Answer 51

- Chemical disinfection processes use powerful oxidising chemicals to inactivate or destroy the pathogenic micro organisms e.g chlorine, chloramines, chlorine dioxide, ozone Chemical disinfection will inactivate most pathogenic micro-organisms present in water - Physical disinfection processes remove or deactivate the pathogenic micro-organisms Physical processes for the disinfection of water either rely on energy input for the inactivation of pathogenic organisms or physical separation of the organisms from the water e.g UV irradiation, fine membrane filtration

Answer 52

1 - Bacteria cell 2- ozone molecule on the bacteria cell wall 3- ozone penetrates the cell wall 4- ozone oxidises the cell wall 5- bacteria cell after it has come in contact with a number of ozone molecules 6- cell destruction (lysis)

Answer 53

The amount of chlorine used up by the water the pathogens themselves exert little chlorine demand other substances present when the chlorine is added may use significant amounts in oxidation reactions dissolved organics especially naturally colour substances forming unwanted DBPs ammonia - high chlorine demand

Wastewater Content Flashcards

(79 cards)