How To Treat Organic Waste With The Bio-Stab

Transcription

1 VergärungRosRoca AT The Bio-Stab-Process Anaerobic treatment of organic waste from municipality or industry Ros Roca Internacional S.L. Plochinger Str. 3 D Esslingen Tel Fax Introduction The treatment of organic waste from municipalities or industry with the Bio-Stab-digestion technology is meanwhile tested in numerous industrial reference plants and has proven its efficiency. A multitude of organic waste fractions characterized by different water contents, contents of impurities and degrees of acidity can be treated. Some of these waste fractions are listed following: Household waste Biowaste from source separated collection Industrial organic waste from: - food processing industry - markets - slaughter houses - fat collectors The Bio-Stab-process is a wet digestion technology which makes possible the separation of impurities before the biological treatment by means of mechanical separation without hand-sorting. Due to the very effective separation of the impurities, the composts are of high-quality and are characterized by a low salt and a high organic content. The biogas produced by the digestion is energetically used for the operation of the digestion plant. Most of the electricity produced can be fed to the elctric network. The waste water is cleaned according to the regulations, normally with sequence-batch-reactor-technology (SBR). Composting systems for the treatment of the compost-like residues are offered in accordance to the location and the degree of maturation

2 Page 2 of 9 The advantages of the treatment of organic waste with the Bio-Stab-process are summarized following: Technology proved in numerous industrial reference plants Completely automatized waste processing in a closed system Production of high-energy biogas Production of electricity Low odour emissions Very effective separation of impurities before the biological treatment A wide range of waste can be treated independently of their humidities, the content of impurities and the degree of acidity Production of high quality compost with a low salt content Simply designed digestion reactor without mechanical driven parts ROS ROCA INTERNACIONAL is the exclusive licensee of the Bio-Stab-process in Western Europe (exception Italy) since April The process was developed from ATU Ingenieurgesellschft für Abfalltechnik und Umweltschutz located in Munich. The reference-list shows the Bio-Stab-plants realized in the last years. References Location Capacity Sort of waste Status tons/year Avila, E Presorted household waste Start-up 2002 Boden/District of Westerwaldkreis, D Biowaste In operation since 1999 Münster, D Biowaste In operation since 1997 Schwabach, D Biowaste In operation since 1996 Kaufbeuren, D Biowaste In operation since 1992

3 Page 3 of 9 3 Description of the Bio-Stab-Process Following the Bio-Stab-process is explained with the example of the newest plant which is in operation in Boden (Germany, District of Westerwald) since the begin of The plant treats municipal source separated organic waste and additionally has the possibility to treat organic industry waste. The process is shown in the flow chart and explained more detailled hereafter. Flow-sheet Bio-Stab-Digestion plant Boden (Germany) Capacity tons per year Biowaste Kitchen waste Dosing bunker Buffer tank Iron metals Magnetic separator Green waste to composting plant Screen Mill Waste suspenser Hygienization Process water Light fraction Screen Heavy fraction Grit trap Heat Digestor Biogas Gas storage Co-generation Fresh compost to agriculture Centrifuge Electricity Water treatment Waste water to sewage treatment plant

4 Page 4 of 9 The organic waste is delivered by trucks in a closed reception hall including a flat bunker to store the organic waste for a certain time. With a wheel loader the pretreatment line of the process is loaded. Liquid organic waste from industry can be pumped directly in a heated storage tank. The dry mechanical pretreatment of biowaste is a disc screen to separate fermentable and non fermentable material. Non fermentable material is further treated in a composting plant. Fermentable material passes a mill to reduce the particle size before being further treated by wet pretreatment. The wet treatment of the Bio-Stab-process contains two waste suspenser, the hygienization and a succeeding processing step to remove impurities. Waste suspenser and hygienization tanks In the suspensers the organic fraction is well mixed with process water which is recycled from the digestion process. Here the biodegradable organic fraction is pulped until it is a homogeneous suspension with a solid matter of 8 10 %. For a following hygienization of the whole suspension hot process water is used in the suspenser. The suspenser is a cylindrical steel vessel equipped with a special stirrer. The flow conditions caused by the stirrer produce shear forces that cut the organic constituents while the non fermentable components are affected only insignificantly.

5 Page 5 of 9 The suspenser process is divided in thress main steps: Feeding with organic waste and process water Mixing and suspending Evacuation One batch cycle in the suspenser needs minutes. Then the waste suspension is evacuated into a hygienization tank. There are no pumps necessary to evacuate the suspenser.in the hygienization tanks, which are equipped with stirrers, the suspensions stays minimum 1 hour at a temperature of more than 70 C according to the requirements of the german biowaste regulation. One of the main advantages of the Bio-Stab-process is the possibility to remove with high efficiency impurities like plastic, stones, glass, bones, sand by an automatically operated system including a wet screening and a sedimentation process. It is very important to remove all the impurities to guarantee a troublefree digestion (no sedimentation and clogging in pipes, heat exchangers), low maintenance costs (reduction of wear, abrasion) and a high compost quality. This type of wet pretreatment including the hygienization process gives to the plant operator the possibility to use digested suspension directly as liquid fertilizer or the solids after the dewatering as fresh compost. It is not necessary to install further equipment to clean the compost. The two process steps are integrated in a stainless steel container. Rake and sand grit trap

6 Page 6 of 9 The suspension flows first through a fine screen with a size of 15 mm. Non fermentable material and impurities bigger than this size are removed by the screen. An integrated screening press transports the screen fraction out of the container, dewaters and compacts the rake fraction. The press water is led back into the process. The suspension with particles smaller than 15 mm passes the screen into the grit trap. Here the heavy fraction (glass, stones, sand) settles and is transported against the flow direction with a screw conveyor. To improve the function of the grit trap an aeration is installed. At the end of the horizontal screw the heavy fraction is transported out off the trap with a grit classifier into a container. This system to remove the impurities is characterized by a low electric power consumption and is operated without pumps wearing out. The cleaned waste suspension is then flowing to a buffer tank and after cooling down to the process temperature continuously fed into the digestor for anaerobic treatment. The Bio-Stab-process uses a single step digestion under mesophilic conditions in a cylindrical steel tank. Single step mesophilic digestor (V=3.500 m 3 ) The main parameters of the digestion process are summarized following: Hydraulic retention time days Solid concentration 4 8 %

7 Page 7 of 9 Organic loading 4 8 kg organic solids / (m 3 of reactor volume * day) Biogas quality (CH 4 ) Vol.% Biogas production Nm 3 /t The parameters organic loading, biogas quality and biogas production depend on the kind of organic waste which is treated in the digestor. The digestor is well mixed with biogas which is very important to avoid solid sedimentation and to guarantee best process conditions in relation with ph, temperature and nutrient concentration. The gas mixing system consists of a stainless steel piping distribution which is installed central inside the digestor and a compressor installed in the machine hall rising the biogas pressure. The produced biogas is buffered in a gas storage and used directly after dehumidification by co-generation. Gas storage tank Main advantages of a single step, mesophil digestion process: simple process technology high process stability under mesophilic conditions minimal thermal energy consumption cooling of waste water is not necessary low ammonia emission of solids after dewatering

8 Page 8 of 9 For the dewatering of the suspension a centrifuge is used. Here the suspension is separated into a solid and liquid flow. The solids have a solid matter of % and are used directly as fresh compost in agriculture. The limiting values for impurities and heavy metals are clearly remained and are the result of a very effectiv pretreatment process. Process water which is mainly recycled within the process is cleaned by means of a sequence batch water treatment process (SBR). Water treatment plant (SBR) The SBR-process is a technology combining biological and mechanical steps in one reactor. After filling the SB-reactor the process water is mixed and aerated whereas ammonium is converted to nitrate (nitrification). By denitrification nitrate is converted to nitrogen under anoxic conditions without aeration. After sedimenation of biomass a part of clarified process water is used again in the waste suspenser. Surplus water leaves the process to the sewage treatment plant.

9 Page 9 of 9 Odour loaded air from the bunker and the machine hall is collected and cleaned by srubber and biofilter technology. The total amount of ait which is collected and cleaned biologically is m 3 /h. Scrubber and biofilter for cleaning of odour loaded air \Medien\Broschüren und Vorträge\Vergärung\Vergärung Englisch\VergärungRosRoca.doc Recived from Dr. Korz after Biogastudy / visit in Boden on Intermediated by KILDESORTERING SFK Ingeniör Arne Tronstad N 2480 Koppang Tel.: Faks: Epost: a.tronstad@online.no