Interactions between wastewater and sludge treatment
Operation and intensification of wastewater treatment plants
Participating persons:
Bengt Hultman, Professor
Erik Levlin, PhD
Elzbieta
Plaza, Assoc. professor
Jozef
Trela, PhD
Monica
Löwén, researche engineer
Project period: 1997-2004
Finansing: VA-forsk and others.
Summary
Possibilities to use sludge as a product for different purposes
is dependent on the interest from other sectors as industry (use
of apatite as raw material for the phosphate industry), energy sector
(use of biogas), agricultural and food sector (acceptance for use
of sludge on agricultural land), transport sector (use of methane
gas for vehicle fuel) och waste sector (combined treatment of sludge
and wastes for product recovery). Sludge as a raw material is influenced
by factors as consumer behavior, connections of industries and design
of the wastewater system (combined or separate system, sorting of
waste streams inside houses etc).
Product recovery from sludge gives rise to a large number of side-effects
due to changes of sludge composition (as the inorganic fraction),
that side-streams may be formed with high concentration of organic
materials, ammonium and phosphate and that separate treatment can
be made to produce for example nitrification bacteria which may
be seeded into the activated sludge process for the main stream
and phosphate compounds. A significant emphasis was laid on description
of these side-effects as a scientific basis to evaluate different
methods for product recovery. The project performance was connected
with works by three research students (Puhua Li, Liisa Piirtola
and Jozef Trela). Studies were done in parallel on product recovery
as master thesis works with special emphasis on phosphorus recovery
from sludge.
The project showed that several methods are possible to improve
the operation and decrease operational costs if increased consideration
is given to interactions between wastewater and sludge treatment.
Different examples are:
- Recycling of sludge with a high fraction of inorganic material
to the activated sludge process to improve the sludge sedimentation
properties
- Supply of organic materials (for instance produced by hydrolysis
of sludge) to improve the denitrification efficiency
- Seeding of nitrification bacteria from a separate step with
a high influent ammonium concentration (as supernatant from
dewatering of digested sludge) to the activated sludge process
for the main stream
- Use of biological phosphorus removal technology to later facilitate
the phosphorus recovery from sludge
- Mechanical, biological and chemical treatment of excess sludge
to decrease sludge production and foaming and to increase biogas
production in anaerobic digestion (Hultman
and Levlin, 2003).
Reports
The work have been reported in VA-Forsk
2004-15.
References
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