Biogas production and usage in Kaunas Sewage plant

 

      

 

Summary

Kaunas Sewage plant is a subsidiary of Kaunas Water Supply Utility named Kauno vandenys Ltd. The plant is situated on the edge of the city, called Marvelė, on the bank of  Nemunas river. It was started in September, 1999, being the first sewage plant in Kaunas history, despite of the fact that the city is the second by size in the country with population of 415,000. Up to this year, municipal wastewater was simply issued to Nemunas. Treatment on the Sewage plant is carried out by mechanical and chemical systems. The main treatment technology is anaerobic digestion of sewage. Also, the sludge is processed by dehumidification technology.

Lithuanian construction company KAUSTA built the plant in 1996-1999, using the loan from European Reconstruction and Development Bank, EBRD. Because of high quality of construction works and its unique installations, the plant was awarded the title of Best Lithuanian Product of the Year (1999). The advanced techniques and special equipment were used in the construction, including equipment and experience of the Finland’s largest corporation YIT – Corporation. It enabled the company KAUSTA to reduce the thickness of concrete walls from 150 cm to 40 cm,

the latter being capable to withstand the same huge pressure of sludge stored.

 

Treatment parameters of Kaunas Sewage plant.

There are 4 sedimentation tanks installed, each of 52 m of diameter, and 4 methane-tanks, each of 18 m of diameter and 10,000 cubs of volume. The total capacity of plant is 232,000 cubs of wastewater per day. In a previous year the daily average issue of treated wastewater was 63,000-70,000 cubs. The digestion process is mezophylic one. Practically, only one methane tank is operated at present.

Currently, the purification capability achieved can be described by following parameters:

removal of suspended matters:  78 - 83%,

removal of matters as BOD7:  60 - 67%,

removal of  phosphorus: 70 -  82%.

total removal of organic waste: 11- 14 tons/day.

 

Biogas production and sales.

The combustion of biogas recovered in methane tanks was started in June, 2000 in the own boiler-house of the plant. The total output of biogas, 10,000 cubs per day, significantly exceeds the own heating needs.  At present 28¬35% of biogas recovered is burnt at the boiler-house in winter season, the rest is burnt in a torch.

To avoid a useless combustion of biogas in a torch, a special project of biogas supply has been implemented. It is a pipeline project which provides the delivery of biogas to Noreikiškės boiler-house owned by Kaunas district heating company Kauno energija Ltd. Noreikiškės is a settlement situated in a close vicinity of the Sewage plant. It is planned to cover as much as 10 % of total expenditure of Sewage plant by income from biogas sale to Noreikiškės boiler-house.

The project has the following relevant parameters:

biogas hourly delivery:     up 350 m3;  

route length:        1,400 m;

diameter pf plastic pipeline:         110 mm;

biogas pressure: 3 bar;

total investment: 1 million LTL, split to

300,000 LTL for pipeline and route,

500,000 LTL –for compression station,

180,000 LTL – erection cost; 

20,000 LTL – for receiver .

The pipeline was started in December, 2001. The Sewage plant sales the biogas to Kauno energija Ltd. by tariff 200 LTL/1000m3.

 

Biogas parameters of Kaunas Sewage plant.

Lithuanian energy institute had analyzed the samples of waste water collected at Kaunas Sewage plant (2000). The laboratory tests and data processing lead to following results:

content of dry organic matter in influent waste water:      2.19 – 3.34%;

the same , in effluent waste water (at the outlet):             1.37 – 2.06%;

content of CH4  in biogas recovered:     70 – 75%;

content of CO2 in biogas recovered:       25 – 30%;

content of H2S in biogas recovered:        5 – 25 ppm;

biogas output : 6000 – 10000 m3 /day;

calorific value of biogas recovered:         25.06 – 26.85 MJ/ m3.

Thus, the analysis proved the high quality of biogas recovered.

 

Co-generation unit for Sewage plant.

As biogas recovery at the plant is expected to grow because of the biological treatment and network extension project, Lithuanian Energy Institute suggests to install the small-scale co-generation unit (CHP) at the plant. Own hourly peak demand of winter months ranges from 600 to  1,000 kW (thermal) and from 170 to 200 kW (electric). The input-output and efficiency parameters of recommended unit are as follows:

 

Electric output
(kW)

Heat output
(kW)

Gas consumption (m3.h-1)

Biogas consumption (m3.h-1)

Electric efficiency (%)

Heat efficiency (%)

Total efficiency (%)

150

226

45.5

65.0

34.8

52.6

87.4

 

Financial parameters of the project seem to be quite attractive:

investment costs (USD): 70,300

interest rate:        12%

maturity period:   10 years

dynamic pay back time (year):     2.2

annual operating costs (USD/kWhel):       0.0057

sale price (USD/kWhel): 0.0392

 

Biological treatment and network extension project.

 In 2000, Kauno vandenys Ltd started to implement the significantly bigger project, with a budget of 100 million Litas. The project is aimed at construction of biological treatment facilities and extension of city’s water supply and sewage networks. The idea of this project is to increase the input of wastewater to the Sewage plant by connecting the local water supply and sewage networks of neighbouring settlements and villages to city’s central networks, respectively. It will result in reduction of pollution of open waters and ponds by city’s waste water up to the level set by national environmental norm LAND 10-96. This norm was established by Lithuanian Environment Ministry and conforms to requirement of Helsinki Commission HELCOM. The recovery of biogas is assumed to increase significantly, as well as degree of waste biodegradation.

The breakdown of investment is estimated to be 80 million Litas and 20 million Litas for biological treatment facilities and extension of networks, respectively.

The Lithuanian Council of ISPA had included the project to the list of ISPA projects (ISPA is EC structural instrument for pre-accession). According to preliminary financing scheme, ISPA provides a subsidy of 50 million Litas. Lithuanian Government provides the second subsidy, 20 million Litas. The rest part of project’s budget, 30 million Litas, will be covered by bank loan.

The construction works will be started in midyear of 2002 and finished in 2004.