Speaker: Nikhil Gampa
The addressing of the challenges prevalent in Unnao required design innovation optimizing of land requirement for FSTP and operations and maintenance. There were two distinct kinds of technologies that were present in the market, i.e. nature-based system and in the other end of the spectrum was the mechanical system (conventional ones including thermal). This complex challenge led us to combine the treatment technologies from both approaches. The wastewater generated after dewatering was treated using DEWATS of the nature-based and the sludge was dewatered using the mechanical system –leading to the birth of a hybrid system for treatment of faecal sludge.
Unnao is a centrally located city of Uttar Pradesh(India) situated on the Gangetic plain between the other two major cities Lucknow and Kanpur. It is one of the major industrial hubs and is among the most densely populated city in India with a total population of about two million.
The geographic position of the city had fueled its growth over the last couple of years. As per the 2011 Census, Unnao has recorded a population growth of 15.11% as compared to the population in 2001.The streets remained constricted, and the wastewater generated is managed at the household level by means of onsite sanitation systems.
Tthe majority of the households rely on on-site sanitation systems such as septic tanks and pits to contain and partially treat faecal sludge that is generated. The city has been declared open defecation free, and it was increasingly critical to manage and treat the faecal sludge which is made from these onsite sanitation systems.
A faecal sludge treatment plant was, therefore, the need of the hour to curb the dire effects of unregulated and unscientific disposal without treatment of faecal sludge in the city.
But the very high population growth in the city had led to a huge burden on land making the land availability difficult and a scarce resource. The inorganic growth led to very limited time availability for planning and implementation of the FSTP and to a unique situation where there is a very low area availability per capita but very high sludge generation rate. This requires a big(capacity) treatment plant within a smaller footprint area with affordable/low O&M.
The addressing of the challenges prevalent in Unnao required design innovation optimising of the land requirement for FSTP and the operations and maintenance(O&M) including the skill required. There were two distinct kinds of technologies that were present in the market, i.e. naturebased system which relied on passive anaerobic digestion and drying beds: They cost/ higher CapEx and have a higher land requirement, but OpEx was less. These were easy to understand and operate. In the other end of spectrum was the mechanical system (conventional ones including thermal) which costs less(CapEx) and occupied low area but was complicated and required lot of energy and resources for O&M.
This case study discusses how a hybrid treatment system has been piloted and demonstrated in Unnao city for the treatment of faecal sludge along with the aspects of the design of hybrid FSTP.
The main treatment steps followed in the treatment of faecal sludge are solid-liquid separation, stabilisation, and dewatering of sludge and pathogen removal through separate treatment for solid and liquid components. The treatment modules for solid components are: Screen Chamber, Thickening tank, Stabilization Reactor, Screw press, Drying platform with leachate collection and for liquid components are: Equalization tank, Integrated Settler with Anaerobic baffled reactor(ABR) and Anaerobic filter(AF) chambers, Planted Gravel Filter (PGF), collection with Sand & Carbon filter followed by a collection tank/Polishing pond(PP).
The modules under the hybrid system have the following advantages:
(a) Optimized Land requirement, site preparation costs and civil construction costs: The Hybrid system will reduced the need of several sludge drying beds and as well as the area required for drying. Also, the land/site preparation costs in terms of excavation and filling costs are also reduced.as one can use the existing topography of the land available. In the hybrid system, the civil structures are reduced as mechanical dewatering is being used which minimises the requirement of SDB/replaced with a drying platform with leachate collection.
(b) Optimised treatment time: In the hybrid treatment system, due to mechanical dewatering, the time required for stabilisation and drying of faecal sludge is reduced, thereby optimising the treatment time.
(c) Upskilling requirement: Skill requirement for operations and maintenance of the hybrid treatment system is on a higher level than nature-based treatment system but can be easily upgraded with a minimal upskilling of the operator.
The Unnao FSTP(32 KLD) having a hybrid treatment system was constructed within less than half the area and with lesser CapEx than that of a nature-based FSTP having the same capacity.