Grade 2 - Solids Handling and DisposalREVISED

7/29/2019 Grade 2 - Solids Handling and DisposalREVISED

1/30

Sludge Disposal Methods


2/30

Digestion of Sludge Aerobic

Anaerobic


3/30

Aerobic Digestion Biological sludge treatment process

Employs aeration to stabilize waste sludge

Reduces total volume of sludge by aerobicbacteria that breakdown volatile solids

Creates condition that forces the

microorganisms to use their own cellularmass as a food source

Process requires a source of aeration


4/30

Aerobic Digestion Operates either on a batch or continuous

basis

Supernatant may be drawn off to allowadditional sludge to be added

Solids concentration entering the digester

may run 0.5 to 1.0 percent


5/30

Aerobic Digestion Control Factors Dissolved Oxygen

0.5 to 2.0 mg/L

Temperature > 50 degrees F

Solids Retention Time > SRT the > volatile solids reduction )

pH carbon dioxide produced from digestion reduces the pH

best if kept at 7.0

Organic Loading (> OL = >DO levels needed )


6/30

Anaerobic Digestion Absence of Oxygen

Most economical option if the process produce

energy by using methane Stabilized sludge is relatively inert


7/30

Anaerobic Digestion 3 Stages 1st - Extracellular enzymes ( outside cell)

breaks down solid complex organics

2nd - Acid formers ( acid production and acidregression stages ) microorganisms convert

products of first stage to organic acids &

carbon dioxide & hydrogen

3rd - Methane forming bacteria converts

hydrogen and carbon dioxide to methane


8/30

Anaerobic Digestion - Methane Formers Controls the process

Sensitive to environmental factors ( pH ,

temperature , toxins ) Reproduce very slowly

Easy to kill and difficult to grow


9/30

Anaerobic Digestion Uniformity and consistency in operations

Sudden changes can inhibit performance

Raw sludge is blended with recirculateddigester sludge

Two criteria that determines capacity , is

hydraulic detention time & volatile solidsloading rate


10/30

Anaerobic Digestion Hydraulic detention time

15 to 20 days

Organic loading

0.1 to 0.4 lbs. VS/cu.ft./day


11/30

Anaerobic Digestion Types Fixed Covers - number of different

constructions

Floating Covers - Floats directly on the liquidsurface


12/30

Anaerobic Digestion Heating

Systems Maintaining a constant temperature for

methane-formers is one of the most important

control functions Heat is required to maintain digester

temperature and to heat incoming sludge


13/30

Anaerobic Digestion - Temperature

Ranges Psychrophilic

50 to 68 degrees F

50 to 180 days

Generally not very effective Mesophilic

85 to 100 degrees F

25 to 30 days

Most popular Thermophilic

120 to 135 degrees F

5 to 12 days

Mostly used for class A sludge


14/30

Anaerobic Digester - Foaming Fine bubbles of gas trapped in a semi-liquid

matrix

Commonly forms during start-up and whenthe digester is under stress

Start-up ( carbon dioxide to methane ratio is not

equal )


15/30

Sludge Processing Concentration and stabilization of sludge prior to final

disposal

Methods thickening stabilization

conditioning

dewatering

Purpose is to reduce potential problems from pathogens

quality of undesirable organic material

potential for odor problems

reduce vector attraction


16/30

Sludge Processing Thickening

increases solids content by removing excess

water promotes efficient sludge digestion

Methods

gravity

solids content of 1- 3 %

dissolved air floation

solids content 2 - 8 %


17/30

Sludge Processing Stabilization - reduces organic matter in sludge to a

more stable form

Methods

thermal

applying heat to drive away water

lime stabilization

applying lime until pH of 12 or higher for 2 hrs

aerobic & anaerobic digestion Composting

microorganisms break down organic matter to a humus-

like material


18/30

Sludge Processing Composting

windrow

mechanical

Suitable environment must be established &

maintained for bacteria to survive

Blending

aeration temperature


19/30

Sludge ProcessingFactors affecting composting

sludge type

initial moisture content uniformity of mixture

frequency of aeration or turning

climatic conditions

desired moisture content of final product


20/30

Sludge Processing Dewatering - removes liquids

Drying beds

solids concentration up to 40% used for well digested, stabilized residuals

Centrifuges

solids concentration 20 to 40 %

rotates liquids at high speeds & spins the water away


21/30

Sludge Processing Vacuum Filters

solids concentration 15 to 30 %

rotating filter media passes through vat of residuals,

residuals coat the filter and water is extracted by vacuum,

polymers may be used

Pressure filters

solids concentration up to 50%

series of verticle plates,belts,or frames, water squeezed

out under pressure, solids are retained between the belts

or plates


22/30

Sludge Reuse or Disposal OptionsIncineration

burning sludge at high temperatures in

furnace volume is reduced

ash is stabilized

requires air permit & pollutant removal high operating costs

complex


23/30

Sludge Reuse or Disposal OptionsLandfill

disposal of sludge in a lined landfill

leachate collection required odor potential

local regulatory requirements

inexpensive

trucking costs


24/30

Sludge Reuse or Disposal OptionsSurface disposal

trench, waste pile, lagoon

biosolids remain longer than 2 years monofills

surface impoundment

dedicated disposal sites


25/30

Requirements for Sludge Surface

Disposal Systems without liners

have pollutant limits for arsenic,chromium, andnickel

must have leachate collection system and monitorleachate

systems with covers have methane limits

cannot be in the 100yr. floodplain, wetland, orarea with geologic faults

requires an NPDES stormwater permit


26/30

Requirements for Sludge Surface

Disposal Special restrictions on crops and grazing

public access restricted for 3 years after

closure groundwater monitoring

pathogen and vector reduction requirements


27/30

Sludge Reuse or Disposal OptionsLand Application

application of sludge to condition the soil or fertilize

crops / other vegetation

sprayed or spread on soil surface

tilled into soil or injected directly below the surface

must be applied at agronomic rates, meet pollutant

limits, and pathogen & vector attraction reductionrequirements

requires 30 days or more of storage


28/30

Sludge Reuse or Disposal Options sites must be evaluated for soils, depth to

SHWT,depth to bedrock,buffer requirements

application rate limited by type of crop to be grown

application events must be timed to coordinate withfarmers schedules

records must be maintained & submitted to DWQyearly

requires certified operator requires large amounts of land

odor potential


29/30

Sludge Reuse or Disposal Options Distributing & Marketing : composted sludge

given away or sold in bulk

must achieve class A sludge end use is not regulated

bag or bulk compost


30/30

Sludge Reuse or Disposal OptionsPathogen & Vector Attraction Reduction

two levels of pathogen reduction are

recognized by both EPA and DWQ class B or PSRP

class A or PFRP

vector attraction reduction

reducing the attractiveness of sludge to

flies,mosquitoes,fleas,rodents, and birds

Grade 2 - Solids Handling and DisposalREVISED

Documents

Transcript of Grade 2 - Solids Handling and DisposalREVISED