sludge incineration. There are a variety of dewatering processes available:
(a) vacuum filtration; (b) centrifuge; (c) belt filter press; (d) plate and frame
press; (e) sludge drying beds or infrared sludge dryer; and (f) sludge lagoons.
Sludge drying beds: It is a sludge dewatering process using solar energy to
evaporate water from the sludge slurries.
Sludge handling: It includes every required processes or management regarding
waste sludge, such as sludge thickening, sludge dewatering, sludge digestion,
sludge storage, sludge transportation, sludge disposal, etc.
Sludge lagoons: It is an earthen basin used for holding and dewatering sludge
slurries by solar energy.
Sludge thickening and dewatering combined, belt filter press: Conditioned
sludge is first placed on a gravity drainage section where it is allowed to thicken.
In this section, the bulk of the free water is removed from the sludge by gravity.
On some units, this section is equipped with a vacuum assist, which enhances
drainage and may help to reduce odors. Following gravity drainage, pressure is
applied in a low-pressure section, where sludge is squeezed between opposing
porous cloth belts. On some units, the low-pressure section is followed by a highpressure section where the sludge is subjected to shearing forces that induce the
release of additional quantities of water from the sludge. The final dewatered
sludge cake is removed from the belts by scrapper blades.
Sludge thickening/dewatering centrifuge, basket centrifuge: They are suitable
for small plants. It is a semi-batch type operation. Sludge cake is collected on the
sides of the spinning bowl, while the centrate (dilute effluent stream from the
centrifuge) overflows the bowl rim. Once solids have built up to a maximum
thickness, the feed sludge is stopped, and scrapper blades peel the sludge from the
walls. The process is then resumed.
Sludge thickening/dewatering centrifuge, solid bowl centrifuge: Sludge is fed at
a constant flow rate into the rotating bowl where it is separated into a dense cake
and a dilute stream called centrate. The units can be used with no prior chemical
conditioning, but solids’ centrate quality are improved considerably when the
sludge is conditioned with polymer.
Sludge thickening: Sludge thickening is the first step of sludge handling. It is
employed prior to subsequent sludge dewatering processes to increase the efficiency of the sludge dewatering equipment. There are at least five types of sludge
thickening processes: gravity thickening, flotation thickening, centrifuge thickening, gravity belt thickening, and rotary drum thickening.
Sludge volume index (SVI): SVI is the ratio of the volume (in mL) of sludge
settled from a 1000 mL sample in 30 minutes to the concentration of mixed liquor
(in mg/L) multiplied by 1000. It indicates settling capabilities and compaction,
and it is an indication of filamentous organism overgrowth and several other
indicators of process problems.
Sodium hypochlorite: It is a liquid sodium hypochlorite solution to be used as a
disinfectant for water or wastewater disinfection.
158
L. K. Wang et al.
(a) vacuum filtration; (b) centrifuge; (c) belt filter press; (d) plate and frame
press; (e) sludge drying beds or infrared sludge dryer; and (f) sludge lagoons.
Sludge drying beds: It is a sludge dewatering process using solar energy to
evaporate water from the sludge slurries.
Sludge handling: It includes every required processes or management regarding
waste sludge, such as sludge thickening, sludge dewatering, sludge digestion,
sludge storage, sludge transportation, sludge disposal, etc.
Sludge lagoons: It is an earthen basin used for holding and dewatering sludge
slurries by solar energy.
Sludge thickening and dewatering combined, belt filter press: Conditioned
sludge is first placed on a gravity drainage section where it is allowed to thicken.
In this section, the bulk of the free water is removed from the sludge by gravity.
On some units, this section is equipped with a vacuum assist, which enhances
drainage and may help to reduce odors. Following gravity drainage, pressure is
applied in a low-pressure section, where sludge is squeezed between opposing
porous cloth belts. On some units, the low-pressure section is followed by a highpressure section where the sludge is subjected to shearing forces that induce the
release of additional quantities of water from the sludge. The final dewatered
sludge cake is removed from the belts by scrapper blades.
Sludge thickening/dewatering centrifuge, basket centrifuge: They are suitable
for small plants. It is a semi-batch type operation. Sludge cake is collected on the
sides of the spinning bowl, while the centrate (dilute effluent stream from the
centrifuge) overflows the bowl rim. Once solids have built up to a maximum
thickness, the feed sludge is stopped, and scrapper blades peel the sludge from the
walls. The process is then resumed.
Sludge thickening/dewatering centrifuge, solid bowl centrifuge: Sludge is fed at
a constant flow rate into the rotating bowl where it is separated into a dense cake
and a dilute stream called centrate. The units can be used with no prior chemical
conditioning, but solids’ centrate quality are improved considerably when the
sludge is conditioned with polymer.
Sludge thickening: Sludge thickening is the first step of sludge handling. It is
employed prior to subsequent sludge dewatering processes to increase the efficiency of the sludge dewatering equipment. There are at least five types of sludge
thickening processes: gravity thickening, flotation thickening, centrifuge thickening, gravity belt thickening, and rotary drum thickening.
Sludge volume index (SVI): SVI is the ratio of the volume (in mL) of sludge
settled from a 1000 mL sample in 30 minutes to the concentration of mixed liquor
(in mg/L) multiplied by 1000. It indicates settling capabilities and compaction,
and it is an indication of filamentous organism overgrowth and several other
indicators of process problems.
Sodium hypochlorite: It is a liquid sodium hypochlorite solution to be used as a
disinfectant for water or wastewater disinfection.
158
L. K. Wang et al.