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SYLLABUS (As per CBCS Scheme)

Module -4:

Biological Treatment Process: Suspended growth system - conventional activated sludge process and its modifications. Attached growth system – trickling filter, bio-towers and rotating biological contactors. Principle of stabilization ponds, oxidation ditch, Sludge digesters(aerobic and anaerobic), Equalization., thickeners and drying beds.

8 Hours

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Module Planning

Class 01	Biological Treatment Process
Class 02	Suspended growth system
Class 03	Conventional activated sludge process and its modifications
Class 04	Attached growth system – trickling filter
Class 05	Bio-towers and rotating biological contactors
Class 06	Principle of stabilization ponds, oxidation ditch
Class 07	Sludge digesters(aerobic and anaerobic)
Class 08	Equalization., thickeners and drying beds

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WASTE STABILIZATION POND (WSP)

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WASTE STABILIZATION POND (WSP)

Advantages:

Simplicity

simple to construct
simple to operate and maintain
only unskilled labour is needed

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Low Cost

cheaper than other wastewater treatment processes
no need for expensive equipment

High Efficiency

BOD removals > 90%
Total nitrogen removals is 70-90%
Total phosphorus removal is 30-45%
Efficient in removing pathogens

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Types of WSP

Anaerobic pond
Facultative pond
Maturation pond

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Maturation Pond

1-1.5 m deep
Receive the effluent from a facultative pond
Primary function is the removal of pathogens

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Design of WSP

1. Anaerobic Pond

Volumetric BOD loading (g/m³d)

------- (1)

Where

Li = influent BOD, mg/L (=g/m³)

Q = flow, m³/d

= anaerobic pond volume, m³

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should lie between 100 and 400 g/m³d

to maintain anaerobic conditions

to avoid odour release

The mean hydraulic retention time (HRT), t_a (day) is determined from:

--------- (2)

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Design values of permissible volumetric loading on and percentage BOD removal in anaerobic ponds at various temperatures

Temperature (^oC)	Volumetric loading (g/m³d)	BOD removal(%)
<10	100	40
10 – 20	20T – 100	2T + 20
>20	300	60*

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2. Facultative Ponds

Surface BOD loading (λ_s, kg.ha d)

------ (3)

where

Af = facultative pond area, m²

λs = 10LiQ/Af

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OXIDATION DITCH

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A sludge digestion tank is a RCC or steel tank of cylindrical shape with hopper bottom and is covered with fixed or floating type of roofs.

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Types of Anaerobic Digesters

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What is a Sludge Drying Bed ?

Fertiliser for agriculture

Sludge drying beds

Faecal Sludge

Septic tank

Aqua priviy

Latrines

Biogas plants

Anaerobic baffled reactor

Trickling filters

Co-composting

Conveyance

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What is a Sludge Drying Bed ?

Sludge drying beds can be

Unplanted
Planted

Unplanted sludge drying beds

Design similar to unplanted filters sand/gravel filters
Require desludging after every cycle of drying (manpower required)

Planted sludge drying beds

Design similar to reed beds or vertical constructed wetlands
Do not need desludging after every cycle:

Porosity is maintained by the root systems of the plants.
Sludge is transformed into biomass (plants) and can be harvested.

Source: STRAUSS & MONTANEGRO 2004

Planted

Unplanted

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Unplanted Drying Bed

Source: SASSE (1998)

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Planted Drying Bed

Source: TILLEY et al. (2008)

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Examples

Unplanted drying bed at a waste stabil- isation pond (WSP) site in Colombia.

Source: IRC (2004)

Source: EAWAG/SANDC (2008)

Unplanted drying beds in Ghana (Sandec)

Covered sludge drying bed at the Arcata wastewater treatment plant (USA)

http://www.humboldt.edu/arcatamarsh/compost.html

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Examples

Source: EAWAG/SANDC (2008)

New installation of a constructed wetland with ventilation pipes at the Asian Institute of Technology (AIT) in Bangkok, Thailand

Primary sludge drying bed and reed bed (in the background).

Source: MUENCH, E.,von 2009)

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