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Bekkelaget Wastewater Treatment Plant

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1 Bekkelaget Wastewater Treatment Plant
From Pollution to Solution First of all we are delighted and honored to host you here at Bekkelaget WATP and I wish to extend a warm welcome I would like to express my profound gratitude to the organiser of this event. My name is Rashid Abdi Elmi and I will be your host and I will first to give a short presentation and then take your for a tour inside the Rock Cavern and then our biogas upgrading plant. Bekkelaget WWTP has a long history, the first plant was enacted in 1963, Several upgrading have been undertaken since then. Plant was situated at the spot where we are now. The decision to upgrade and to include nitrogen removal process at Bekkelaget WWTP was taken The plant was the placed inside the rock caverns. The plant was completed and came into full operation in year 2000. Bekkelaget Wastewater Treatment Plant Rashid Abdi Elmi



4 Holmenkollen ski jump arena
Rock caverns Gas holder Admin building

5 Sewage as a resource Sewage Treated wastewater
Improving water quality and biodiversity in the Oslo fjord – due oxygen rich effluent Biogas Upgraded fuel - Fuel for public transportation Zero CO2 emission/carbon neutral Sludge for agriculture farmland Fertilizer 140 tons phosphorus per year ( bags of mineral fertilizer , 30 kg/bag) Energy extracted from wastewater 250 GWh for District heating: apartments, 12,000 kWh/yr pr apartment . Reduction CO ton, corresponds to the emission from private vehicles We all tend to think of sewage as an unpleasant problem that has to be dealt with. It's time to rethink. We in VAV regards sewage as a resource. 1. The impact of treated wastewater. Before the creation of the new Bekkelaget Wastewater Treatment in 2001, the condition along Bekkelaget basin was often characterized with high content of hydrogen sulphide water and generally poor oxygen conditions. However since 2001, the oxygen concentration has significantly improved from 50 meters deep (deep discharge of treated wastewater) and up to meters (approximate innlagringsdyp for the diluted wastewater), ie there has been a direct positive effect of the discharge from the new treatment plant. Since the beginning of 2011 the high goals for oxygen concentrations have been fulfilled down to 60 m depth. Since May, the oxygen concentration exceeded down, although it remains high concentrations down to 50 m with 2.02 ml / l at 50 m depth. At 60 and 70 m depth however, the oxygen concentration dropped to 0.6 and 0.37 ml / l (ie, less than high target at 60 yards and less than intermediate target at 70 m). 2. Biogas. The sludge drier was terminated due high maintenance and operational cost than previously anticipated. Furthermore the employees were subjected to a poor working environment due particles pollution in the plant. Secondly farmers also preferred dewatered sludge than the dried sludge because of the fertilizing value is lower in the case of the sludge from the drier. New APEX directives introduced in 2007 would have required large investment in order to satisfy the demands concerning explosion and security. The termination of the sludge drier led to even more amount of biogas being torched. This was unacceptable to the Oslo water and sewerage works. An environmental impact assessment study was initiated to investigate the best alternative usage for the excess amount of biogas generated at the BWWTP. An environmental impact analysis was carried out. Four alternative were evaluated and was later conducted Production of biomethane for bus operations with heat pumps for internal heat requirements was found to be environmentally sound. Four alternatives were investigated but only two alternatives i.e. 2 & 4 were evaluated in which special attention was given to CO2 emissions and energy considerations. The four alternatives are as follows: Present operations with sludge dryer shut-down. (The gas is used for internal heating). Installation of a gas generator for electricity production. Production of heat for a remote/district heating network. Production of biomethane for bus operations with heat pumps for internal heat requirements

6 City of Oslo – main sewer system
Bekkelaget WWTP VEAS WWTP Prepared enabling change


8 Cavern dimensions 212 m Water treatment Inlet tunnel
Screens, sand and grit removal Primary settling/ direct precipitation Bio step, activated sludge Clarifiers Extra space(not in use) Sand filters Sludge treatment Digesters Ventilated air treatment – odor control Biogas, upgrading (out) 12

9 Discharge consent – Compliance limit
New discharge consent from : Nitrogen: 70% of all nitrogen must be removed Phosphorus: 90% of all phosphorus must be removed Organic matters: 70% of organic matters as BOD5,must be removed And the total amount of overflow must be less than 2% of the total loads of nitrogen, phosphorus and organic matters NB: The population growth coupled with climate changes resulting to increased to both hydraulic and pollutant loads poses as daunting challenge in meeting present and future stringent discharge compliance limits.

10 Treatment capacities – operational modes
Dry weather flow 1450 l/s or approx m3/d – it is subjected to biological and chemical treatment with filtration as final step (max capacity 1900 l/s) Nitrogen, phosphorus and organic matters are removed Flow rates between l/s is treated chemically and partly filtration (< 3000l/s) Phosphorus is removed and organic matters is partly removed Flow rates between l/s is treated through 3 mm screens: Objects such Objects such as rags, paper, plastics, and metals are removed in order to prevent damage and clogging of downstream equipment, piping, and appurtenances

11 Wastewater treatment process- Flowchart Biogas Upgrading Plant
Primary sludge Buffertank Buffer Silo Bio sludge Dewatering Thickener Digester Biogas Overflow Magasin~35.000m3 4000 l/s < Q < 6000 l/s Sand, grit and screenings FeSO4 PAX-18 Activated sludge Clarifier Primary Filter PAX-18 Primary Precipitation 1900 l/s<Q< 4000 l/s Mixed liquor recycle Oslo fjord Q<1900 l/s Q=1900 l/s Sludge recycle Belt Thickener Preliminary treatment (Screen) Preliminary treatment, or screening, is the first step in cleaning wastewater. Before the raw sewage is introduced into our plants, large contaminants such as rocks, rags, toys, and golf balls must be removed. Primary (mechanical) treatment is designed to remove gross, suspended and floating solids from raw sewage. It includes screening to trap solid objects and sedimentation by gravity to remove suspended solids. This level is sometimes referred to as “mechanical treatment”, although chemicals are often used to accelerate the sedimentation process. Primary treatment can reduce the BOD of the incoming wastewater by 20-30% and the total suspended solids by some 50-60%. Primary treatment is usually the first stage of wastewater treatment. Many advanced wastewater treatment plants in industrialized countries have started with primary treatment, and have then added other treatment stages as wastewater load has grown, as the need for treatment has increased, and as resources have become available. The pretreatment removes large floating objects Such items could plug pumps, fill treatment channels, and damage moving equipment parts. Mechanically cleaned barscreens accomplish this task, removing the offensive material, and depositing it into dumpsters for disposal at a landfill. Following screening we use small mechanically mixed basins to remove any grit and sand-like material before the wastewater is routed to primary treatment. The main purpose of Grit Chamber or sand and fat trap: To protect moving equipment To reduce formation of heavy deposit in pipeline, channels and conduits To reduce the frequency of digester cleaning causes by excessive accumulation of excessive of grit. The removal of grits (sand, gravel and fat ) is essential a head of other processess. Secondary (biological) treatment removes the dissolved organic matter that escapes primary treatment. This is achieved by microbes consuming the organic matter as food, and converting it to carbon dioxide, water, and energy for their own growth and reproduction. The biological process is then followed by additional settling tanks (“secondary sedimentation", see photo) to remove more of the suspended solids. About 85% of the suspended solids and BOD can be removed by a well running plant with secondary treatment. Secondary treatment technologies include the basic activated sludge process, which use biological activity to break down organic matter Main purpose with chemical precipitation is to remove phosphorus When adding a metal salt to wastewater its called chemical precipitation. In wastewater (and water) treatment this is normally an iron or aluminum salt The metal salt build flocks with the phosphorous and particles in the wastewater Simplified equation: Me3+ + PO43- = MePO4 At Bekkelaget WWTP chemical precipitation is used at normal flow as simultaneous precipitation by adding ferrous sulfate, and during high flow periods as direct precipitation by adding PAX in one part of the primary settling tank To improve flock building polymer is added during direct precipitation. Tertiary treatment is simply additional treatment beyond secondary The related technology can be very expensive, requiring a high level of technical know-how and well trained treatment plant operators, a steady energy supply (aeration), and chemicals and specific equipment which may not be readily available. An example of a typical tertiary treatment process is the modification of a conventional secondary treatment plant to remove additional phosphorus and nitrogen. Skilled operators are needed to monitor and maintained the right condition in order for accomplish removal BOD and nutrients. Blowers are used to inject air needed by microorganism to breakdown the organic matter and oxidize ammonia through nitrification. Biogas Upgrading Plant

12 Nitrogen removal – Biological treatment processes
Influent Sewage Organic nitrogen - Urea Ammonia nitrogen NH4 Nitrate N0-2 N0-3 Nitrogen gas N2 O2 1st Step Nitrification 2nd Step O2 Denitrification Organic carbon (carbon source)

13 Sludge treatment process
Thickening Reduces the content of water in sludge to reduce hydraulic load on the digesters. Primary sludge thickened in belt thickener with polymer Bio sludge thickened in centrifugal thickening with polymer Digesters Thermophilic anaerobic digestion process, whereby the incoming sludge is pre-heated before entering the digesters Digestion in the digesters , at 55 °C in 15 days Dewatering Reduces the content of water in sludge to reduce transport costs Centrifugal dewatering with polymer (30-35% DS) Sludge storage tanks Acts as buffer in order to obtain uniform loading of the system and stores sludge during unexpected failure system. Sludge Production Generated at the plant is approximately tons DS/yr the advantages are: short retention time, reduction in organic substance, considerable increase in production of biogas and finally the sludge is pasteurized and stabilized sludge is the end product.

14 Facts and Goals for the City of Oslo.
CO2 emissions from private and public transport is approximately % of the total emissions in the city of Oslo. The City of Oslo’s main goal is: To cut 50% of greenhouse emissions by the year 2030.


16 LP COOAB ® process – Low Pressure CO2 Absorption
Gas tank Gas drier High pressure compressor Activated coal - filter 200 bar CO2 0,5 bar 2 bar Odorizing the bio-methane Chemical scrubbing Chemical scrubbers use amine solutions. Carbon dioxide is not only absorbed in the liquid, but also reacts chemically with the amine in the liquid. Since the chemical reaction is strongly selective, the methane loss might be as low as <0.1%. Part of the liquid is lost due to evaporation, and has to be replaced. The liquid in which carbon dioxide is chemically bound is regenerated by heating. Two types of compounds are used: mono ethanol amine (MEA) and di-methyl ethanol amine (DMEA). If hydrogen sulphide is present in the raw gas, it will be absorbed in the amine scrubber solution and higher temperatures will be needed for the regeneration. Therefore it is advisable to remove it before absorption in the amine scrubber. The Upgrading Process descriptions: Incoming raw biogas, depending on production source, is saturated with water, contains H2S and is slightly pressurised. In most cases the pressure must be increased to overcome the pressure loss over the upgrading system. Hydrogen Sulphide H2S Removal When the H2S concentration is above 500 ppm, a two stage H2S removal system will be applied. In the case of BRA, the H2S concentration is lower than 500 ppm, therefore only activated carbon is applied. The H2S is removed to very low concentrations, typically below 0.5 ppm. Elementary sulphur will be formed by the process and adsorbed on the activated carbon. Traces of oxygen in the raw biogas or a very small air dosing ensure sufficient oxygen for the process. The activated carbon is replaced when saturated with sulphur. Approximately 99.5 % of H2S is removed. CO2 removal. CO2 is removed in a counter current packed absorption column. CO2 enters the column at the bottom and recirculated Cooab liquid is sprayed from the top. The CO2 removal is a fully reversible chemical absorption process and the specially composed amine absorbs more than 99.5 % of the CO2. The biogas with more than 99.0 % methane leaves the column from the top. The CO2 enriched Cooab liquid is pumped to the CO2 stripper. CO2 stripping The CO2 enriched Cooab liquid is warmed by heat exchange and enters the packed counter current stripper column from the top. As warm Cooab vapour rises from the lower part of the column, the chemical absorption will be reversed and CO2 released. Gaseous CO2 will leave the stripper column from the top and the Cooab vapour will condensate. In the bottom of the column the Cooab liquid is heated above its boiling point by steam injection. The lean Cooab, free from CO2, is cooled down and recirculated to the CO2 absorption column. The high purity of the CO2 stream makes is suitable for use as cooling agent, in green houses and other CO2 applications CO2 removal/ COOAB recovery

17 Produced upgraded biogas (biomethane)

18 Biomethane value chain
Producer End Biomethane Money flow

19 Exhaust emission and noise
S/N Units Diesel Bio-methane Reduction % NOx g/km 8.1 1.9 78 Particulate matter 0.3 0.005 98 CO2 kg/km 2.6 100 Noise dBA 111 92 Advantages in using biomethane are as follows: Biogas will give lower exhaust emissions than fossil fuels and so help to improve local air quality Biogas fuelled vehicles can reduce CO2 emissions

20 The potential of Biomethane in Oslo
Oslo kommune Vann- og avløpsetaten The potential of Biomethane in Oslo Oslo: p.e – 12 million Nm3 biomethane Buses Personal vehicles Sewage sludge 150 – 200 6 000 Household organic waste 8 000 Total 14 000

21 62 64 66 240 1100 2000 Source: AGA-Linde

22 Net Energy production

23 Green Emission for chemical consumption

24 Total Greenhouse Emission

25 Challenges facing Bekkelaget WWTP
This include among others; Population growth in Oslo is taxing Bekkelaget wastewater treatment Plant and creating a need for new plants. Oslo will have in the range of 1.1 million inhabitants (including Nittedal municipality) in This represents a population increase of 18-25% since 2009 (Figure). Bekkelaget WWTP was dimensioned for p.e. in 2000, in 2013, Bekkelaget serves p.e. Climate change – Many of the earliest sewer systems were combined sewers, designed to collect both sanitary wastewater and storm water runoff in a single system. Increased Hydraulic Loads hence increased pollutant loads (NTot and PTot ). Stringent discharge consent for 70 % Nitrogen and 90 % phosphorus removal including overflow and the total amount of overflow must be less than 2% of the total loads of nitrogen, phosphorus and organic matters

26 Expansion of Bekkelaget WWTP

The increase of the hydraulic loading of a municipal wastewater treatment plant caused by the sludge dewatering process is of minor importance. However, the rejected nitrogen load accounts for up to 25% of the nitrogen load in the raw sewage

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