Simple to construct, operate and maintain
Does not involve installation of expensive electro-mechanical equipment
Operates on a combination of solar energy and natural forces and thereby has very low O&M costs.
Extremely robust and can withstand hydraulic and organs shock loads
Effluents from maturation pond are safe for reuse in agriculture and aquaculture.
Can reliably produce high quality effluent with low BOD, SS, Fecal Coliform and high DO levels.
BOD reduction of the order of 90% and more
Suspended solids reduction is somewhat less due to possible overflow of algae
Coliform reduction could be upto 6 long units
Total nitrogen removal between 70-90%
Total phosphorus removal between 30-45%
In case of unlined ponds, soil and geo-hydrological survey during planning stage to assess risk of groundwater contamination.
Sulphate concentration in raw wastewater under 300 mg SO4/L to avoid odour nuisance.
Suitable under warm Indian climatic conditions
For areas with easy availability of land
In areas with social preference for aquaculture
In areas with low, unreliable or expensive power supply.
L.2 Duckweed Pond System (DPS)
Natural and simple wastewater system involving sheltered pond like culture clots
A large pond subdivided into smaller cells through floating bamboo or other material to break the wave and wind action.
Extremely rapidly growing floating duckward vegetation serving as a dynamic sink for organic carbon, dissolved nutrients and minerals.
Thick mat of duckweed out competing and inhibiting growth of other aquatic plants.
Pond functioning as a facultative lagoon with deeper layers under anaerobic environment.
Retention period in the system 7-21 days
Continuous process requiring intensive management for optimum production.
Yield of large quantities of proteinaceous matter as fish feed or as a supplement for animal feed.
Can meet Indian discharge standards for BOD and SS. Removal of Ammonical nitrogen (N) and Dissolved Phosphates (P) is also substantial.
For settled wastewater, BOD and SS below 30mg/L are attainable at 12 detention.
High nutrient and mineral removal due to uptake by duckweeds.
Primary treatment including screening, grease trap, grit removal and sedimentation.
Preferably the influent BOD, SS and ammonia to be under 80 ppm, 100 pm and 50 ppm respectively.
A series of smaller cells of around 10m x 10m to 10m x 30m to break the continuum in the pond (cell size as a function of wind speed, pond size and wave action.
Cell borders made with floating bamboo mats or PVC profiles to shelter from wind and wave action
Impermeable lining of clay or artificial liners in case of pervious and fractured strata
Outlet structure with variable weir height
Nitrogen loading of around 9 km/ha/day
Small size culture ponds for duckweed seeding and as fish nursery ponds.
Duckweed drying and processing unit in case of large harvest and for sale as animal feed
In case of downstream aquaculture ponds – introduce suitable species of fishes e.g. Grass Carp., Common Carp, Silver Carp, Rohu, Mingal, Cattle and freshwater prawns.
Low strength domestic wastewater or after primary sedimentation with influent BOD – 80mg/l
In combination with existing WSP
Rural and semi urban settlements with easy land availability
As a polishing pond for an existing activated sludge plant or other technology based STPs
L.3 Facultative Aerate Lagoon (FAL)
Simple flow scheme without primary or secondary settling and sludge recirculation
Deep lagoon with anerobic bottom layer and aerobic top layer.
Simultaneous degradation of sludge in the bottom and dissolved organics in the top layer.
Lower energy input corresponding to requirement for maintaining only desired DO levels in the top layer and not for creating completely mixed conditions.
As per the information in literature based on Indian experience the following performance is expected from a well-functioning aerobic lagoon:
BOD removal 70-90%
Suspended solids removal 70-80%
Coliform removal 60-99%
Typical hydraulic detention time 3 days or more
Depth between 2-5 m depending on local soil and groundwater conditions
Effective outlet structure with baffles and stilling basin to prevent solids overflow.
Standalone system for sewage treatment
As a pre-treatment unit for WSP
As an up-gradation option for overloaded WSPs.
L.4 Trickling Filter (TF)
A proven 100 year old technology
Rugged system with simple and silent operation
Lower process monitoring requirement as compared to ASP
Consistent effluent quality.
Performance of a slow rate trickling filter is comparable to ASP
Standalone treatment for sewage if operated at slow rates
As a high rate roughing filter for high BOD wastewater.
In combination with ASP for good and consistent performance
L.5 Activated Sludge Process (ASP)
Key features
Proven and tested for more than 7-8 decades all over world
Several modifications possible to meet specific requirements.
Very good performance in terms of BOD and SS. Treated effluent can most often satisfy the current Indian effluent discharge standards. Performance is critically dependent on sludge settling characteristics and design of secondary clarifier. Sludge settling characteristics are typically influenced by bio-flocculation which in turn depends on growth rate of micro-organisms. Growth rate is generally controlled by controlling biological solids retention time / food to micro-organism ratio.
Un-interrupted power supply for aeration and sludge recirculation
Maintenance of biomass concentration in the aeration tank and proper settling in the secondary clarifier.
The most widely used option for treatment of domestic wastewater for medium to large towns where land is scare.
L.6 Biological Filtration and Oxygenated reactor (BIOFOR) Technology
Enhanced primary treatment with addition of coagulants and flocculants.
High rate primary tube settlers and integrated thickening offering space economy.
Two stage high rate filtration through a biologically active media and with enhanced external aeration.
Co-current up flow movement of wastewater and air enable higher retention and contact.
Treatment scheme excluding secondary sedimentation but recycling of primate sludge.
Deep reactors enabling low land requirements.
A compact and robust system.
Suspended solids and BOD removal of 90% and 70% respectively in the primary clarifier.
High quality effluent with BOD 10mg/L and total system efficiency of 94-99.9%
Low turbidity with suspended solids under 15 mg/L and total system efficiency of 98%
Pathogen removal of 2 on the log scale.
Addition of alum as coagulant (~@60 ppm)
Polyelectrolyte for high rate sedimentation (~@0.2-0.3ppm) in tube settlers.
Special and patented granular filter media `Bioloite’ made of clay.
Backwash of BIOFOR bed and recycle of the wastewater.
Treatment (digestion) and disposal of sludge from clarifier (not provided at the STPs due to space limitations)
L.7 High rate Activated Sludge Biofor –F Technology
Key features
In general, high level of mechanization and sophistication
The flow scheme excludes primary sedimentation tank
Superior aerated grit chamber and classifier
Circular aeration tank with tapered air diffusion system
Second stage aeration and rapid sand filtration through a biologically active filter media
Dissolved air floatation for sludge thickening.
Digester hearing and temperature controller anaerobic sludge digestion.
Mixing of digester contents through biogas.
Dynamic cogeneration of electrical and thermal energy through gas engines.
L.8 Fluidized Aerated Bed (FAB)
A compact and robust system involving extended aeration process with submerged aeration
Biomass growth on fluidized bed of plastic media enabling retention of biomass and long solid retention time in the reactor leading to low food to `micro-organism ratio’ and higher organic removal.
Two stage biological oxidation
Flexibility in handling organic load by adjusting quantity of fluidized media
Reactors upto 5 m deep enabling low land requirements
Tube settlers again offer space economy
Ability to withstand limited organic overload
Special grade plastic proprietary media custom made for offering high specific surface area
Diffused aeration system
Submerged stainless steel screens at the outlet of FAB reactors to prevent media overflow
Tube settlers for compact clarifier.
Options
Addition of coagulant and polyelectrolyte for compact plants
Tertiary treatment of chlorination
Sludge treatment through thickner and bag filter press or drying beds.
High BOD removal with effluent concentration under 10mg/L
High suspended solids removal with effluent concentration under 20mg/L
Faecal coliforms removal of the order of 2-3 log scale at FAB-2 stage.
The FAB technology based system is particularly applicable for:
Small to medium flows in congested locations
Sensitive locations
Decentralized approach
Reliving existing overloaded STPs.
L.9 Submerged Aeration Fixed Film (SAFF) Technology
Essentially a trickling filter with enhanced oxygen supply through submerged aeration
Unconventional plastic media offering high void ratio and specific area compared to stone and aggregates.
Large biomass and long solid retention time in the reactor leading to low `food to micro-organism ratio’ and higher organic removal.
Two stage biological oxidation
Treatment scheme excluding primary sedimentation and sludge digestion
Reactors upto 6 m deep enabling low land requirements.
Tube settlers again offer space economy.
The SAFF technology based system is particularly applicable for:
Small to medium flows in congested locations
Sensitive locations
Decentralised approach
Reliving existing overloaded trickling filters.
L.10 Cyclic Activated Sludge Process (CASP)
Essentially activated sludge process operated in batches through auto control
Aeration and settling in one tank leading to lower plant foot print
Savings in air/oxygen supply and hence energy
Two levels of treatment possible depending on the requirement
Treatment scheme excluding primary sedimentation and sludge digestion
Complete reliance on auto control, uninterrupted power supply is a must
Diffused aeration system
Several moving parts
High BOD removal of 98% with effluent concentration under 10mg/L
High suspended solids removal with effluent concentration under 20mg/L
Faecal coliforms removal of the order of 2-3 on log scale.
The Cyclic Activated Sludge Process (CASP) may be applicable for:
– Small to medium flows in congested locations
– Sensitive locations
Decentralized approach
Reliving existing overloaded trickling filters.
L.11 Upflow Anaerobic Sludge Blanket Process (UASB)
Key features
No mechanical components or external energy requirements in the reactor, therefore process not vulnerable to power cuts
No primary treatment, suspended solid in the wastewater serve as carrier material for microbial attachment.
Recovery of gas with high calorific value
Low sludge production
Relatively simple routine operation and maintenance
Biological activity can be restarted without any external seeding or special care after interrupted operations.
An UASB reactor can bring down the BOD of the domestic wastewater to 70-100 mg/L and suspended solids (TSS) to 50-100 mg/L. However, sludge washout from the reactor is possible and effluent BOD and TSS is very high during such episodes. The effluent is strongly anoxic with high immediate oxygen demand (IOD). Should not directly discharged into water bodies or used for aquaculture or irrigation without re-aeration.
Use of anticorrosive materials / paints on exposed surfaces
Frequent cleaning / de-sludging of distribution / division boxes and influent pipes
Skilled supervision during start-up and for control of biomass levels within the reactor
Post treatment of the UASB effluent is invariably required.
Control of toxic materials and sulfates in the wastewater is required for efficient operation.
The suitability of this technology may be doubtful as a stand-alone secondary treatment option.