Aerobic and Anaerobic Aerobic and Anaerobic Reactor ConfigurationsReactor Configurations

Biochemical EnvironmentBiochemical Environment

Aerobic Conditions: Oxygen is used as electron acceptor

Anoxic Conditions: Nitrate is the electron acceptor

Anaerobic Conditions: absence of oxygen and nitrate and organic compounds are converted to biomass, CO2, CH4 and H2S.

Organic matter + H2O CH4 + CO2 + NH3

+ H2S+ new cell

Why anaerobic TreatmentWhy anaerobic Treatment

Process stability

Produced Methane can be used to produce energy

Produced amount of excess sludge is about 10 % of aerobic treatment. Hence, reduction of waste disposal cost

Low nutrient requirement (BOD/N/P is 100/5/1 for aerobic; 700/5/1 for anaerobic mo.s

No air supplementation, so lower operational cost

No off-gas air pollution

Biodegradation of aerobic non-biodegradable

Seasonal treatment is appropriate

Possible disadvantages of anaerobic Possible disadvantages of anaerobic TreatmentTreatment

long startup Alkalinity should be sufficient Under mesophilic conditions, optimum

temperature is 35 ºC Nitrification not possible Low kinetic rates at low temperature

If COD < 1000 mg/L anaerobic treatment is not practical economically

Effluent from anaerobic treatment is generally not acceptable for direct discharge and aerobic polishing step is needed.

Anaerobic Bioreactor

Aerobic Bioreactor

Waste ?

wastewater

Equilization basin

Anaerobic Reactor ConfiguratiosAnaerobic Reactor Configuratios

Anaerobic Contact Stabilization: CSTR with cell recyle under anaerobic conditions. Well-mixed reactor suspended growth Before settling tank a gas separator is used to make

settling easierAdvantages:Simple and inexpensiveDisadvantages:System is not stable for shock loading and toxic

compounds Settling is problem

Anaerobic FiltersAnaerobic Filters

Attached growth systems

In this type of reactor, waste enters in the bottom and flows through the rocks or plastic media used for biomass immobilization.

Recirculation is used to dilute any toxic compound in the influent.

The main limitations of reactor : accumulation of solids in the packing material (plugging). So, wastes containing high amount of suspended solids are not suitable for A.F

channeling

cost of packing material

Table.1. Some Studies on the treatment of industrial Table.1. Some Studies on the treatment of industrial wastewaters using A.F.wastewaters using A.F.

Type of wastewater

Tempr. (°C)

Organic Loading Rate (kg/m3.d)

HRT (h) Removal efficiency

Sugar industry

35-37 - 12-36 55%

Distillery wastes

35 15 72 90

Chemical process

37 12-15 22-30 80-90

leachate 37 0.2-0.7 30-40 d 90-96

Upflow Anaerobic Sludge Blanket Reactor Upflow Anaerobic Sludge Blanket Reactor (UASB)(UASB)

This type of reactor was developed to avoid the main problems of

the anaerobic filter.

Flow is in upward direction.

Biomass settles in the bottom usually in the forms of granule.

Advantages:

High biomass concentrations. Hence high organic loading rates can be applied.

so excellent COD removals due to high biomass concentrations.

Compared to Anaerobic filter, wastewaters with higher suspended solid concentrations can be applied.

Disadvantages:

Sludge granulation is complex and not fully understood process

Biomass escape at the effluent at higher loading rates hybrit reactors are used to avoid this problem)

Fluidized and Expended Bed ReactorsFluidized and Expended Bed Reactors

Effluent

Glassbeads

carrier

wastewater

Water-jacketedglass reactor

RecirculationpumpORP, pH

probes

gasIn these systems microorganisms grow on small inert particles such as fine sand or activated carbon

High Recycle ratios are used to keep the particles in suspension

The rate of liquid flow and the resulting degree of expansion of the bed (10-25%) determine whether the reactor is a fluidized or an expanded (less expansion) bed reactor

limitation: high and uniform upflow so high pumping cost

Table 2. Some treatability studies using UASB

Type of wastewater

Influent COD

OLR (kg/m3/d)

Temperature C

HRT (h) % COD removal Efficiency

Beer industry

1000-1500

4.5-7 20-24 5 75-80

Agricultural waste

11 000 2-5 30 48 70-65

Slaughter hause

2000-3500

4 30 19 85

Paper industry

1000 5 - 49 75

Sugar industry

4000-60000

20-25 28-32 - 92-95

Aerobic Treatment SystemsAerobic Treatment Systems Activated sludge Process (CSTR with/wo

cell recycle)

Contact Stabilization

Oxidation Ditch

Sequencing batch reactor (SBR)

Extended Aeration

Step feed

Contact Basin

wastewater

Secondary

clarifier

Stabilization Tank

mixing

Air

Sludge waste

Contact stabilization

Fill

React

Settle

Draw

Idle

SBR

No settling tank, no sludge pumping

Aerobic/anoxic/anaerobic cycles for

nutrient removal

process flexibility for bulking

Tolerant to shock loading

No washoutsludge

Oxidation DitchOxidation Ditch

Nitrification and denitrification is also possible

Typically operate in an extended aeration mode