Wastewater Flashcards

Question

Compare 3 screen types

Answer 1

Bar screens - Have poor capture and can suffer from wear but continuous spray cleaning is not needed Band screens - high removal, essential for more complex plants, preferred type Horizontal rotating drum - Have milliscreens (standard for industry) or suboscreens (for large municipal flows), good capture rates, need continuous high P spray cleaning and hot water blasting for fats

Answer 2

Less organics to landfill Lower odour potential Smaller volumes for transportation

Answer 3

Aerated spiral flow - Consistent removal for a wide range of flows, low organic content in grit, pre aeration reduces septicity, Dis: power required from blower, aeration can drive off smelly volatile substances Detritor (Based on principle of constant velocity)- Adv: Low head loss. Dis: Often difficult to get uniform flow, high organic content of grit, loss of grit disturbed by rake Vortex grit removal. Adv: Removes high % of fine grit, maintains removal efficiency for wide range of flows, no submerged equip requiring maintenance, low footprint, low headloss. Dis: Paddles collect rags, oil and grease accumulate, grit sump clogging, deep excavation or high structure required.

Answer 4

Reduce process volumes to secondary treatment Reduce secondary sludge Reduce secondary treatment aeration Captures nuisance material which help downstream processes run smoothly

Answer 5

A proportion of flow is recycled and saturated with compressed air. As the recycle is released into tank the air is released as fine bubbles, air bubbles attach to solids lifting them to surface, floating material is skimmed off and bottom sludge from settling is also removed. If particulate material has low density it may be more suitable. Can also be combined with acid dosing to 'crack' and remove proteins. Alot smaller surface area required for DAF is one of main advantages.

Answer 6

Attached growth process Series of media discs on a rotating shaft, partially submerged in WW Adv: they don't require an air supply, so less power req, loss headloss Dis: Generally only suitable for small sites, can have uneven biomass loading which can lead to shaft failure.

Answer 7

Attached growth process, WW is pumped above media and trickles down Adv: Simple and reliable, low power input (more than RBC), reasonable effluent quality, low skill requirement for operation. Dis: Land area req, limited control (more than RBC), potential for clogging, odour nuisance Req secondary clarifier

Answer 8

Media is in tank, free to move around reactor | Adv: Can control liquid environment quite readily and hence the processes that are going on

Answer 9

Membrane aerated biofilm reactor. Media is a membrane Adv: Always have o2 right on surface of biofilm and oxygen is depleted as it goes through to bulk liquid phase. Bulk liquid phase is often anoxic - good dentitrification

Answer 10

Typically have reaction tank followed by solids separation with recycled solids back into tank. Microorganisms are maintained in suspension - process air is provided to maintain biomass. Biomass is separated from WW prior to discharge.

Answer 11

Complete mix tanks allow for short circuit paths :( Complete mix can cope with higher strength in flows and can be used in series to achieve greater BOD reduction Plug flow minimises risks of short circuit paths, only used for domestic WW, high strength WW fed into plug flow can cause low DO

Answer 12

- A thickener to produce a continuous underflow of thickened sludge for return to the biological reactor. - A clarifier to produce a clarified effluent - A storage tank to store sludge during peak flows

Answer 13

``` Adv: - No PST - Longer SRT - so low sludge production - Stable sludge - won't stink -Simultaneous denitrification due to areas with low DO concentrations - Can be designed for nutrient removal Dis: - Often poor settling - Longer SRT, higher O2 demand -Sludge doesn't digest well - Can be difficult to control extent of anoxic zones - Large footprint ```

Answer 14

Generic AS system, main reactor is contact tank below is stabilisation tank where RAS is prepped as it enters contact tank. Adv: Lower aeration, lower volume for given SRT Dis: Nitrification is limited by retention is contact stage (not good at nutrient removal)

Answer 15

Absorption-Biooxidation - 2 AS plants 1st one is very high rate, enhanced primary Adv: Good for higher strength influents Dis: Extra space req, higher cap cost

Answer 16

Sequencing batch reactor - no clarifier Fill stage -> React stage -> Settle stage -> Decant stage Adv: Single tank Dis: You only take WW in one stage of this cycle

Answer 17

LE - Anoxic -> Aerobic MLE -> Anoxic -> Aerobic with internal recycle 4 stage Bardenpho - Anox - Aerob - Anox - Aerob Have final aerobic stage to get rid of nitrogen gas so it doesn't cause sludge to float in clarifier. Oxidation ditch

Answer 18

UCT Johannesburg (anoxic tank in RAS line) 5 -stage bardenpho ( Anaerobic stage 1st)

Answer 19

Trickling filter solids contact MBBR/AS IFAS

Answer 20

Removal of particulate material | Reduction of BOD, TP, TN associated with organic solids

Answer 21

``` Rapid gravity (water flows down through support media) - typically used for treating waters from rivers and lakes Continuous flow sand - compact and smaller footprint with a higher loading rate compared to rapid gravity, full covered Disc filters - even smaller footprint, low headloss and low energy input, fully covered ```

Answer 22

Physical - Heat, and UV light Chemical - chlorine, ozone Unit processes - already in plant, like screens and AS

Answer 23

``` Contact time Concentration of disinfectants Intensity and nature of physical agent or means Temperature Types of organisms ```

Answer 24

``` Adv: No disinfection by-products No chemicals - and associated delivery storage and hazards Less operator intervention Dis: Power use and replacement parts ```

Answer 25

A physical process where energy is absorbed by DNA. This causes photochemical damage of DNA/RNA within the organism.

Answer 26

Used to extract specific components from the WW eg priority pollutants

Answer 27

Uses gas permeable membranes to directly supply high purity O2 without bubble formation to biofilm. In conventional AS processes the process efficiency is controlled by availability of air, 90% of this is lost and vented to atm, MABR solves this.

Answer 28

UF or MF replaces most tertiary treatment methods as has good effluent quality

Answer 29

Used for enhancing solids separation in AS reactor. Consists of a bioreactor with suspended biomass and then solids separation by MF or UF membranes Produces good quality effluent better than clarifiers Can be either immersed or external (passed through membranes in series)

Answer 30

``` Adv: -Higher volumetric loading rates and thus shorter reactor HRT -Longer SRT ie less sludge production -Can operate at low DO concs with potential for simultaneous nitrification/denitrification in long SRT designs -High-quality effluent -Less space required Dis: - High capital costs - Limited data on membrane life - Potential high costs of membrane replacement - Higher energy costs - Need to control membrane fouling ```

Answer 31

Adv: - Reduction of sludge production up to 90% - Reduction of space required when using high rate systems - Reduction in energy requirement from aeration - Production of CH4 energy (biogas) -Sludge can be stored unfed for long periods -Granular sludge can have market value Dis: -Effluent often requires further treatment -Nutrient removal is limited to biomass growth -High temps are often required to get necessary reaction rates -Odour potential -H2S yields a poor quality of gas and reduced COD removal

Answer 32

``` Contact BVF CIGAR AN-MBR UASB EGSB IC ECSB ```

Answer 33

``` Suspended solids Toxic components Strength and composition of biodegradable COD Nutrients Temp Presence of alternate electron acceptors ```

Answer 34

Biological degradation of organic solids in the absence of free oxygen

Answer 35

MAD - mesophilic | TAD - Thermophilic

Answer 36

Adv: Increased reduction of pathogens Increased solids destruction and biogas production Less solids for further treatment Less retention time required Dis: Odorous sludge and biogas, additional HXs

Answer 37

Thermophilic followed by mesophilic - Less odour than thermo alone - Less foam than meso alone - Stable operation - Improved dewaterability of digested solids

Answer 38

1. Identify potential land parcels considering elevation, contours, price, neighbours and waterways 2. Investigate soil properties 3. Assess crop conditions (Ryegrass of forests) 4. Water and nutrient balance Know when to irrigate Limit for applying N to land + uptake of nitrogen from crops 5. Irrigation methods Centre Pivot Solid Set Rootzone dripline

Answer 39

Centre Pivot - low cost, bad for contours, large setback Solid Set - higher capital cost and maintenance, good for contours, large setback Rootzone dripline - can be above or below ground, $$, small setback, can operate on contours but difficult to install.

Answer 40

Poor flocculation = poor settling Scum accumulation on surface (these problems affect final effluent quality increasing TSS and BOD)

Answer 41

Flocculation zones - upper deflector preventing the accumulation of scum, lower deflector preventing disturbances in separation and thickening zones Scum baffles - which prevent floating biomass from escaping to the effluent Stamford baffle to direct sludge flow back to separation zone

Answer 42

Preferable to resuse solids where financially viable to conserve the nutrients and avoid consuming landfill space. However there are constraints on discharges to land under RMA Options are to spread on land or combust for energy recovery Ash from combustion can be made into bricks or landfilled Costs of solids handling can be 30-50% of the total WWT cost

Answer 43

Dewatering Pathogen reduction Vector attraction reduction

Answer 44

Have a visual appeal and are favoured for cultural reasons

Answer 45

Aerobic contact processes are characterised by their relatively simple design consisting of a completely mixed digestor (reactor) following by a settling tank or clarifier. The settled solids are recycled back into the process allowing ACP to obtain high solids retention time with a high concentration of solids in the reactor. In UASB systems the wastewater moves up through the reactor. A GLSS device is used to separate and remove the biogas, enhance sludge settling by reducing liquid turbulence in the settler, and prevent expansion of the sludge bed in the digester. EGSB systems are similar to that of UASB. They are characterised by the slight expansion of the sludge bed as a result of high superficial liquid velocities and the lifting action of the gas in the bed. This results in high contact between the sludge and wastewater, and allows for significantly higher loading rates compared to UASB systems