Liquid Waste Test Flashcards

Question

Activated Sludge Process

Answer 1

* Microbial sludge from treatment process are introduced into an aeration tank forming an active suspension of biological solids called activated sludge. * Activated sludge and wastewater = mixed liquor. * Aeration: O2 for organics decomposition * vigorous mixing for microbial/sewage contact. * typically requires about 6 hrs of aeration.

Answer 2

* Instead, growth follows a typical pattern that has a lag phase, exponential phase, maximum stationary phase and death phase. * F/M Food to Microorganism ratio important

Answer 3

* Typically a bed of crushed rock covered with an active slime film of microbial populations which aerobically decompose organics in the wastewater. * primary treated wastewater is sprayed onto the filter surface. -Rocks are 75mm (3 in) so do not filter, but provide a large surface area for microbial contact and biodegradation. -Filter effluent is conveyed to the secondary clarifier.

Answer 4

Remember.. Seconary treatment: * removes 85-95% of TSS and BOD, leaving around 30 mg/l of each in 2o effluent. But not nutrients, pathogens, inorganics, toxic substances.. \*\*Tertiary treatment is generally only used in sensitive environments due to its costliness. ..often doubling the cost of secondary treatment. \*\*mostly applied in wastewater discharges to rivers, lakes or sensitive marine environments.

Answer 5

* Biological nitrification-denitrification * 2 step process (“advanced secondary treatment”) **\*Nitrification** - Secondary effluent (low in organics) sent to alternate (low O2) tank where chemoautotrophic nitrifying bacteria convert **NH3 -\> NO3** (less toxic , but still N) .. Aerobic **\*Denitrification -** Methanol (for carbon source), and O2 added to effluent: denitrifying bacteria convert NO3 -\> N2 (to atmosphere) ... Anaroebic

Answer 6

* Inputs from urine and feces and... synthetic detergents * typically chemical precipitation and coagulation * using Al2SO4 (alum) (also FeCl3, Ca) Al ions react with PO43- to form insoluble precipitate (AlPO4) which settles out. * **Coagulants** can be added at primary or secondary clarifiers or aerated sludge stage.

Answer 7

* Cost effective if you have the land and the time –retention times from 2-3 days to weeks depending on flow requirements. **Increased TSS/BOD reduction** * Prolonged solids settling and biological degradation: native plants, bacteria, algae, and small zooplankton filter nutrients and small particles (**pathogens**) from the water. * Tertiary level lagoons typically aerobic; depth 0.5 to 1.5 m to facilitate photosynthetic algae **( N and P uptake/removal)**

Answer 8

Filtration: Sand filtration Microscreen filtration Membrane filtration Activated Carbon

Answer 9

* Particulate matters are retained in the filter material through straining, adhesion and adsorption. * Constant buildup of particulates decreases flow and increases pressure in system. * **Backflushing** is required to periodically clean filters.

Answer 10

* Sand filtration: can be gravity fed, but typically involve pressurized rapid flow filters, with auto backflushing cycles. * Smaller sand grains provide more surface area and higher removal efficiency, but require more pump pressure and more frequent backwashing. * Most use grain in the range **0.6 to 1.2 mm.**

Answer 11

* Microscreens: woven steel wire mesh as small as **20μm** * Typically screens configured as a rotating drum, with effluent entering into the drum and exiting through the microscreen perimeter.

Answer 12

* Membrane filtration: is a generic term for a number of different, very characteristic separation processes. * Specific pore sizes for target contaminants: Microfiltration ≥ 100 μm Ultrafiltration ≥ 10 nm Nanofiltration ≥ 1 nm Reversed osmosis \< 1 nm

Answer 13

* based on activated carbon adsorption: high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m2,

Answer 14

* Chlorination/Dechlorination * UV Disinfection * Ozone

Answer 15

* Oxidizes cell wall and enzyme constituents * relatively low cost, proven effectiveness in achieving the required pathogen kills. * Residual chlorine is toxic to biota so effluent must be dechlorinated prior to discharge * Regulation requires the residual chlorine is to be limited to 0.01 mg/L (10 μg/L)

Answer 16

* (254 nm) * destroys the nucleic acids in pathogenic organisms, disrupting DNA, disabling vital cellular functions: mutagenic to bacteria, viruses and other micro-organisms. * UV disinfection is most effective in high clarity purified water (i.e. reverse osmosis ) as microorganisms buried within suspended particles may be shielded from the UV light and pass through the unit unaffected. * Highly filtered water also facilitates transmittance of UV throughout the effluent water column.

Answer 17

* very strong oxidant and virucide. Direct oxidation/destruction of cell walls and nucleic acid. * Requires an ozone generator: O3 gas stream is pumped into effluent contact chamber......”bubble stream”. * Ozone is more effective than chlorine in destroying viruses and bacteria. * no harmful residuals that need to be removed after ozonation ; ozone decomposes rapidly. May increase DO due rxns with water * Expensive infrastructure and power requirements

Answer 18

**Sludge** The residuals of suspended solids that form at the bottom of the wastewater treatment clarification tanks. * Under proper circumstances, sludge can be put to beneficial (fertilizer)use...therefore affectionately termed **Biosolids** \*May contain any various levels of metals, toxins, residual pharmaceuticals etc. derived from residential and industrial sewage origins. \*2 classes * **Class A & Class B** \*The sludge is transformed into biosolids using a number of treatments such as thickening, dewatering, drying, and lime/alkaline stabilization. \*Biosolids are initially **3 to 7% solids**, but **may reach 30%** after dewatering and **40% after drying** for 6 weeks....now “liftable”.

Answer 19

* Organic Matter Recycling Regulation (OMRR) \*allow the sludge to be beneficially recycled in accordance with the requirements of this regulation

Answer 20

* Class A: Highest quality biosolids achievable under OMRR; lower fecal coliforms and lower trace elements than * Class B: More liberal application permitted...but not in CRD

Answer 21

* **wishes to establish a Commission for the purpose of administering the Core Area Wastewater Treatment Program.** * The Commission is a separate, project-specific body established by bylaw that oversees the execution of the Seaterra Program. **It ensures the program will be delivered on time, within budget and meet the desired environmental and social outcomes. The Commission oversees the procurement process for all components of the Program.** The Commission operates **autonomously** of the Committee and Regional Board. However, the Commission is required to seek CRD Board and funder approval on pre-determined items as detailed in the CRD bylaw.

Answer 22

Many metals are required in TRACE amounts in living orgasms for enzyme activity, in higher concentrations they are toxic. Heavy metals do not just disappear during treatment, they are either in the resulting water, in the sludge or in residuals after filtering!

Answer 23

Many metals **Bioaccumulate ** in the soft tissues of animals. Once absorbed, compete with other ions and bind to proteins, leading to **impaired enzymatic activity** resulting in damage to many organs throughout the body. **Mercury (Hg):** Causes damage to nervous system, kidneys, and vision. Concern for fetal development **Lead (Pb): ** Causes damage to kidneys, nervous system, learning ability, ability to synthesize protein, and nerve and red blood cells. **Cadmium (Cd):** Causes damage to kidneys. **Arsenic (As): ** Causes damage to skin, eyes, and liver. May also cause cancer

Answer 24

* Commercial inputs * Domestic inputs * Storm Runoff * ....and natural sources (soil erosion)

Answer 25

1. Contributes to effluent aquatic/marine **toxicity** 2. **Bioconcentration effects** limit the ultimate disposal options for stabilized sludge (biosolids) 3. High concentrations of heavy metals in wastewater can cause **toxic shock** to activated sludge ....lowers efficiency...possible restart of system ($)

Answer 26

* Adsorption - Activated sludge - Activated Carbon * Phytoremdiation * Chemical precipitation * Ion Exchange resins

Answer 27

* Entrapment of precipitated metals in the sludge floc matrix * Extracellular adsorption of soluble metals * Assimilation and accumulation of metals within the cell. To be removed, adsorbed metals have to be transferred into the liquid phase...... then the liquid phase treated.

Answer 28

Heller process * Acid combination (HNO3, H2SO4, \*) **solubilizes** heavy metals from sludge, * complexing agents **precipitate** metals from liquid phase, * oxidizing conditions destroys bacterial pathogens and many toxic chemicals(herbicides/pesticides) * Dewatering and pH balancing of biosolids further dilutes remaining metals ........smelter process is one option available to recover the extracted heavy metals

Answer 29

* Various plant species are Hyperaccumulators that bioaccumulate metals from soils/biosolids -mustard plants, alpine pennycress, hemp, ferns, pigweed... * Pros: inexpensive, natural process-low environmental footprint, phyto-mining * Cons: Long term commitment (slow growing) Limited to depth of roots; Food chain concerns.. * ex.. Chinese ladder brake, Indian mustard, Cannabis sativa

Answer 30

* Adsorption using activated carbon is the most efficient classical method * Powdered Activated Carbon Treatment (PAC) * Granular Activated Carbon Treatment (GAC) * removal rate from water can be more than 99% for various metal ions. * Low-cost or bioadsorbents (e.g. zeolite, peat, eggshells, shell fish (chiton)... Incinerated municipal garbage flyash, etc

Answer 31

Powdered Activated Carbon Treatment * Powdered AC added directly to 1o, 2o or activated sludge tanks, becoming a component of the resulting sludge. \*relatively high cost and separation of biosorbents from sludge still a problem (no recycling or regeneration) = “secondary waste”

Answer 32

Granulated Activated Carbon Treatment * Granulated form commonly in filter beds/canisters Granular form relatively easy to collect regenerate and recycle * Three commonly used types of GAC processes: 1. Fixed Bed 2. Multiple Fixed Bed...Series Reactors 3. Pulsed (Moving Bed) System

Answer 33

* Stationary Bed: **BATCH system** * Stationary Bed: **SERIES system** * **Moving Bed: system**

Answer 34

- must be shut down for renewal/backwashing - used in situations with very low influent concentrations and relatively low flows. - Typically gravity fed

Answer 35

- redundant series system; one filter shut down for renewal/backwashing while others remain on line. - produces a higher level of treatment due to passes through multiple filter beds. - also used in situations with very low influent concentrations and relatively low flows....influent under pressure (pumped)

Answer 36

- System can operate continuously without shutdown for media renewal. - Wastewater pumped in through bottom-Fresh AC media constantly fed in from top- spent media removed from bottom and discarded or regenerated - used in high water flow rates and/or high influent solute concentrations applications.-...pumped.

Answer 37

* Thermal regeneration generally involves the following steps: * Drying at 100-150 Co to remove H2O * Volatilization of lighter organics at 150-315 Co * Pyrolysis of heavier organics up to 800 Co * Regeneration of AC up to 1040 Co **Non volatiles (metals)** accumulate and must be disposed of or chemically extracted (by caustic (eg. NaOH) or acid (eg.H2SO4) stripping... more $

Answer 38

* Systems can not tolerate suspended solids in the influent stream (due to **clogging**). - Limited to wastes with low organic concentrations (\< 5%). * High operating **costs** due to carbon costs /system requirements. (AC costs @ $ 800-2000/tonne) * **Disposal** of contaminated carbon can be problematic if it is not regenerated.

Answer 39

* Most common: Precipitation by **hydroxide formation** method....... * Eg. Using **NaOH**, or **Ca(OH)2**, optimum pH 8 – 11 The precipitation typically follows the reaction: Mn+ + nOH- M n+(OH-)n * **Alum** (Al2(SO4)3) added to act as flocculant to enhance settling.........up to 99% removal possible \*Sludges still a problem ...... If metal settling stages not segregated from other process flow sludges.

Answer 40

* Ion exchange resins are water-insoluble polymers which can absorb positively charged ions from solution and release equivalent amounts of other (less toxic) positive ions into the solution. **Removal of \> 99% of metals with selective resins** * The positively charged ions in cationic resins such as H+ are exchanged with positively charged metal ions, in the wastewater. * **Regenerated with strong acid solutions** (used resin typically transported offsite for treatment). (Sludge metals must be acid solubilized prior to Resin treatment).

Answer 41

* Lime Stabilization * Digestion - Aerobic \< 5MGD - Anaerobic \> 5MGD biogas

Answer 42

* *OMRR: Schedule 1** * *Class A Biosolids:** \> pH 12 for 72hrs (\>52 Co for at least 12hrs), then air dried at \>pH12 to 50% solids. Addition of lime **(CaO)**: increases pH up to 12.4 - (cell membranes/pathogens destroyed) - **vector barrier** to infesting flies and insects - CaO has low solubility = persistent, inhibits pathogen regrowth - CaO/H2O reaction **(exothermic)**= to 70 Co......**pasteurization** - high pH reduces solubility and mobility of metals - Ca ions react with sulphur species (eg H2S) to **destroy odors**

Answer 43

* Essentially a continuation of the activated sludge process. Wastewater pumped from 2o clarifier to aerobic digesters * Pros: - Reduction of degradable solids of 40-50% - Lower capital costs/maintenance - Shorter retention times (6-8 days) vs anaerobic (15-20 days) * Cons: Final sludge harder to dewater Indicator organisms often present in final sludge; odors Open tanks have To fluctuations which may reduce efficiency

Answer 44

* Organic matter + H2O CH4 + CO2 + H2O * Pros: - Reduction of solids (25-45%) for disposal or processing - Efficient pathogen reduction - CH4 production...clean fuel for plant power generation - Mesophilic/Thermophilic heat production - reduced odors * Cons: - High capital costs - Organic loads in residual liquid may require treatment. - Longer retention times; 15-20 days

Liquid Waste Test Flashcards

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