The document proposes an anaerobic-aerobic process for treating domestic sewage using LEVAPOR biofilm technology. The process involves pre-treating sewage under anaerobic conditions in a biofilm reactor to reduce energy use and excess sludge production compared to conventional aerobic treatment. Sewage would then undergo post-treatment under aerobic conditions to further reduce pollutants before discharge. This process could achieve up to 75% lower energy use and 67% less sludge than aerobic treatment alone, while also producing biogas as an energy source.

1. Anaerobic-aerobic biotreatment of domestic
sewage by LEVAPOR biofilm technology
Leverkusen, July 2011.

2. 1. INTRODUCTION
The worldwide most practicized method for the treatment of domestic sewage
represents their biotreatment under aerobic conditions ( fig. 1), achieving a remar-
kable removal of main organic and inorganic pollutants, however this process has
also two remarkable problems:
Fig.1 Basic flow diagram of a classical aerobic biotreatment plant
High energy consumption for aeration of the liquid phase with suspended activated
sludge (ca. 0,5 to 0,8 kWh/kg O2-input), representing the highest cost block of a plant
and
High excess sludge production of aerobic processes, which must be treated in a
subsequent step approximately at similar cost level like sewage treatment.
During the biotreatment process, about 40 % of removed COD and 80% of BOD
become converted into low degradable excess sludge, comprising mainly of microbial
cells, digested often under anaerobic conditions, where due to the weakly
hydrolysable microbial cell walls only 25 to 35 % of the biomass can be converted to
biogas, while the residual mass must be conditioned and incinerated, respectively
dumped in landfills.
Anaerobic biotreatment of effluents
represents a nearby energy-autarch alternative method, comprising of acidification
and subsequent methanisation of organic pollutants, generating remarkable amounts
of energy rich biogas under much lower sludge production. Due to their low COD
concentrations and low temperatures during winter periods, this method has not yet
been established in sewage treatment .
With regard to recent developments on energy sector, anaerobic-aerobic treatment of
domestic sewages becomes a very attractive alternative, especially for geographic
ares with elevated average temperatures, like Mediterranian area, Middle-East and
numerous Asian respective American countries.
Biofilm technologies using innovative LEVAPOR carriers, highly adsorbing porous
polyurethane cubes are established since 20 years in aerobic and anaerobic biotreat-
ment of wastewater and polluted gases, their application in anaerobic treatment of
municipal sewage however, has been tested successful in pilot scale.
Aerated basin
Clarifyer

3. 2. PROCESS AND PLANT PROPOSAL
For increasing of plant efficiency and remarkable reduction of treatment costs,
anaerobic sewage pre-treatment in biofilm reactors, followed by aerobic post
treatment in existing aerated basins is recommended.
Fig.2 Basic process flow diagram of anaerobic-aerobic effluent treatment od
municipal effluents by biofilm technology
2.1. PROCESS DESCRIPTION
After a mechanical pre-treatment by a grid and aerated sand trap, raw sewage arrives
into the buffer with variable water levels, where additionally to hydraulic equalisation
a hydrolysis of fine dispersed pollutants and first biochemical conversion of organic
pollutants into volatile fatty acids takes place. From here a constant quantity of
acidified sewage is pumped into the anaerobic reactor, containing active methano-
genic bacterial biofilms, fixed on adsorbing porous LEVAPOR-carrier , enabling a fast
and quantitative microbial colonisation and retention of active cells in the reactor. In
this reactor bioconversion of generated acetic acid into an energy-rich mixture of ca.
2/3 methane and 1/3 carbon dioxide, called biogas, takes place at ambiental
temperatures. The sludge growth in anaerobic process is only 3 to 5% of removed
COD, instead of 35% in the aerobic treatment, resulting in a remarkably better process
economy. Final treatment of residual pollutants occurs in a subsequent aerobic fluidi-
sed bed biofilm reactor, where additionally to COD removal, quantitative nitrification of
ammoniacal nitrogene into nitrate (NO3
-
) takes place. Aerobically treated effluent,
containing suspended biomass leaves the reactor to the clarifier, where sludge flocs
will settle, while retention of LEVAPOR cubes with fixed biofilm occurs by a screen,
installed inside of the reactor.
The obtained biogas can be utilized in a gas-powered combined heat and power unit
for generation of electricity and heat, improving remarkably the process economy and
reducing the CO2-emissions .
Anaerobic
reactor
Aerobic
reactor
Excess
sludge
Biogas
Buffer

4. 3. PLANT DESIGN
3.1. Wastewater data for 150.000 population equivalents (P.E.):
1. Average water flow, Q = ca. 15.000 m³/d = 625 m³/h
2. COD = 18.000 kg/d
3. BOD = 9.000 kg/d
4. TKN = 1.800 kg/d
3.2. Plant design and basic data
a) Equalisation / buffer , VE = 3.000 m³
b) Anaerobic reactor, VANA = 9.000 m³ ( 2 * 4.500 m³)
c) LEVAPOR carrier VLVP= 1080 to 1.350 m³ (12 to 15 vol.%)
d) Aerobic reactor VAE= 2500 m³
e) O2-input GO2 = 7.500 kg/d
4. ESTIMATED PLANT PERFORMANCE
In our tests carried out at room temperature, anaerobic LEVAPOR biofilm reactors
achieved 65 to 75% COD removal, followed by further COD removal and quantitative
nitrification in a subsequent aerobic biofilm reactor. In a pilot plant study of Deutsche
Bundesstiftung Umwelt, (Project nr. 10.144),carried out in anaerobic-aerobic and
denitrifying fixed bed reactors,
 30 to 70 % COD-removal and
 70 % N-removal were achieved, under
 70% lower energy costs and
 67% lower degree of sludge production.
Using LEVAPOR-System, COD-removal rates of 92-96 % and N-removals of 75 to 90%
under 75% lower sludge production can be expected.
PROCESS ECONOMY OF THE PROPOSED TECHNOLOGY
Legend Dimens. Existing aerobic
process
Proposed ANA-
AER-process
Difference
O2-input Kg/d 22.500 7.000 - 69,9 %
Energy consum. Kwh/d 11.300 3.500 - 69,0 %
Biogas m³/d -- 5.985
Energy yield at 6,5 kWh/m³ -- 38.903 + 38.903
Excess sludge Kg/d 9.870 2.893 - 70,7 %
Table 1. Expected results of the anaerobic-aerobic plant
6. ADVANTAGES OF THE PROPOSED LEVAPOR TECHNOLOGY
As mentioned in previous section, in a similar pilot project remarkable savings had
been achieved. Due to the higher surface of LEVAPOR carrier and better mixing in the
planned fluidised reactor, in this project a system with
 Smaller reactor size
 Higher bioconversion rate

5.  Higher biogas production
 Better process economy via biogas utilisation
 Higher process stability will be realised and
 High removal of hazardous micropollutants and endocrine disruptors
 Eventually required nitrogene removal could be achieved in existing reactors.
Due to the estimated realistic advantages, the proposed technology could become a
remarkable efficient alternative for the sewage treatment in warmer climatic areas.
Our additional services
we do offer also our services in designing taylor made problem solutions, based on
40 years experiences on biofilm technologies both in science and in the practice. Our
tools are:
 Analysis of the problem
 Elaboration of alternatives for problem solution , supported by
 Practice oriented biotests (optional),
 Process Design and/or Engineering
 Production and delivery of the required LEVAPOR type and
 Plant startup using optimized mixed biomass, enriched with microbes essential for
degradation.
Presented informations are based on experiences with application LEVAPOR carrier. Testimonies on expected
effects can be made in individual case only on basis of investigations of given emissions and in some cases on
basis of practice relevant experiments.
LEVAPOR GmbH
Kölner Str. 38 Tel.: + 49- 2173-938715
D- 51379-Leverkusen Mobile: + 49- 177-786 5533
Germany www.levapor.com E-mail: levapor@web.de