11 Sludge Hygienisation—A Novel Technology for Urban Areas …
275
[70]. The process parameters in SHRI facility were adjusted while irradiating the
sludge received from the primary settling tank of a WWTP, so that fecal coliform
bacteria present in the sludge were completely eliminated and the residence time
of the irradiated liquid slurry was controlled to prevent their regrowth. Irradiated
sludge was found to be appropriate for using direct disposal in a landfill or for us as
manure after drying. It could also be used as a medium for growing of Rhizobium sp.,
a plant growth promoting microorganism, facilitating the formation of an effective
bio-fertilizer.
Another major industrial-scale sewage sludge hygienisation facility based on Co60 radiation sources was developed at Tucuman in Argentina by PIBA [71]. In this
facility, a concentric source loading tank was located inside the irradiation tank. The
facility was designed to have 32 locations, where a specially constructed support
structure would lodge nine sources in vertical position. Industrial Co-60 sources
(model FIS 60–05) with the average activity of each source ranging between 7 and
10 kCi were employed. As the hygienisation facility was designed for peak radiation
capacity of 700 kCi, therefore, 70 number of Co-60 sources of 10 kCi activity were
needed. At the initial phase, only 8 of the available 32 locations were chosen to place
the radiation sources in the source loading tank, whereas, the other 24 locations were
kept free to facilitate any changes in the arrangements of the radiation sources. The
facility was designed to enable hygienisation of a sludge volume of 140 m
3 /day,
with the batch volume and irradiation time being 6 m
3 and 30 min, respectively [71].
As per the successful bidding, the capital cost of this facility turned out to be USD
3,200,000, whereas, the operating cost for 25 years was estimated to be about USD
4, 69,000.
Recently in March 2019, the first sewage sludge hygienisation plant in the country
became operational in Ahmedabad, Gujarat [72]. This dry sewage sludge irradiation
facility envisages a peak dry sludge load of 100 TPD (tons/day) when it becomes fully
operational [73]. The plant is designed for a peak radiation capacity of 1.5 MCi which
will be provided by the Co-60 sources procured from the Board of Radiation and
Isotope Technology (BRIT)) [74]. However, the source strength will be augmented in
the steps of 150 kCi, looking at the increase in the sludge load. Currently, the facility
hygienises about 6 tons of dry sludge per day and within next 3–4 years, an average
dry sewage sludge load of 30–40 tons/ day is expected [74]. The author visited the
facility in September 2019; and from the discussions with the technical experts it
emerged that the aforesaid hygienisation facility presently receives dewatered sludge
mainly from the Sewage Treatment Plant (STP) of 180 MLD (Million liters per day)
capacity, located at the Pirana Road. On an average, the Pirana Road STP experiences
daily accumulation of 12–15 m
3 of sludge, the weight being in the range of 8–10
TPD. It was also found that the STP treats 160–165 MLD of wastewater. Assuming
uniform composition of raw municipal sewage as a rough estimate, it was found that
for 1 ton of sludge accumulation, about 16.5 Million liters of wastewater needs to be
treated.
It is to be noted that for hygienising the present sludge load of 6 TPD, 150 kCi Co60 pencil is used [73]. The dried sludge is first sent to the crusher and grinder, so that
particle sizes are reduced to less than or equal to 5 mm. The crushed sludge is then
275
[70]. The process parameters in SHRI facility were adjusted while irradiating the
sludge received from the primary settling tank of a WWTP, so that fecal coliform
bacteria present in the sludge were completely eliminated and the residence time
of the irradiated liquid slurry was controlled to prevent their regrowth. Irradiated
sludge was found to be appropriate for using direct disposal in a landfill or for us as
manure after drying. It could also be used as a medium for growing of Rhizobium sp.,
a plant growth promoting microorganism, facilitating the formation of an effective
bio-fertilizer.
Another major industrial-scale sewage sludge hygienisation facility based on Co60 radiation sources was developed at Tucuman in Argentina by PIBA [71]. In this
facility, a concentric source loading tank was located inside the irradiation tank. The
facility was designed to have 32 locations, where a specially constructed support
structure would lodge nine sources in vertical position. Industrial Co-60 sources
(model FIS 60–05) with the average activity of each source ranging between 7 and
10 kCi were employed. As the hygienisation facility was designed for peak radiation
capacity of 700 kCi, therefore, 70 number of Co-60 sources of 10 kCi activity were
needed. At the initial phase, only 8 of the available 32 locations were chosen to place
the radiation sources in the source loading tank, whereas, the other 24 locations were
kept free to facilitate any changes in the arrangements of the radiation sources. The
facility was designed to enable hygienisation of a sludge volume of 140 m
3 /day,
with the batch volume and irradiation time being 6 m
3 and 30 min, respectively [71].
As per the successful bidding, the capital cost of this facility turned out to be USD
3,200,000, whereas, the operating cost for 25 years was estimated to be about USD
4, 69,000.
Recently in March 2019, the first sewage sludge hygienisation plant in the country
became operational in Ahmedabad, Gujarat [72]. This dry sewage sludge irradiation
facility envisages a peak dry sludge load of 100 TPD (tons/day) when it becomes fully
operational [73]. The plant is designed for a peak radiation capacity of 1.5 MCi which
will be provided by the Co-60 sources procured from the Board of Radiation and
Isotope Technology (BRIT)) [74]. However, the source strength will be augmented in
the steps of 150 kCi, looking at the increase in the sludge load. Currently, the facility
hygienises about 6 tons of dry sludge per day and within next 3–4 years, an average
dry sewage sludge load of 30–40 tons/ day is expected [74]. The author visited the
facility in September 2019; and from the discussions with the technical experts it
emerged that the aforesaid hygienisation facility presently receives dewatered sludge
mainly from the Sewage Treatment Plant (STP) of 180 MLD (Million liters per day)
capacity, located at the Pirana Road. On an average, the Pirana Road STP experiences
daily accumulation of 12–15 m
3 of sludge, the weight being in the range of 8–10
TPD. It was also found that the STP treats 160–165 MLD of wastewater. Assuming
uniform composition of raw municipal sewage as a rough estimate, it was found that
for 1 ton of sludge accumulation, about 16.5 Million liters of wastewater needs to be
treated.
It is to be noted that for hygienising the present sludge load of 6 TPD, 150 kCi Co60 pencil is used [73]. The dried sludge is first sent to the crusher and grinder, so that
particle sizes are reduced to less than or equal to 5 mm. The crushed sludge is then