Objective
The project aims at demonstrating that slurry-type wastes originating from the food industry - and a brewery is selected as a typical example - constitute a substantial energy resource. These wastes should therefore not be destroyed by an aerobic, energy-demanding process, but on the contrary be treated in such a way as to recover the energy. Biomethanation is an appropriate process for this, provided innovative adequate pretreatments, namely pretreatments with enzymes, make it possible for methane archae-bacteria to transform the organic matter into methane. Besides, the biogas can be utilized by the industry itself and the pollution abatement constitutes an important fringe benefit.
Due to problems with this system in the actual operation condition are reached only 14% of the planned capacity. The reasons for it are to look for in the reaction of the sludges, which cannot be foreseen in advance, to segregate very fast and to effect aggresively and corrosively against many material. Therefore it must be used a lot of time, to select and test suitable conveying systems and material.
The macerator, used for the comminution has well proved for the comminution of the brewery remains, which, after building in the hardened cutting tools, realized the desired result.
A degradation of the cellulose and lignin parts of the remains could up to now not be effected in the desired manner. It had been tried, by adding enzyme (cellulases) to separate the cellulose. Through no significant difference in the aliphatic acid sample of the hydrolysis was to recognize between sludge after the enzyme treatment and sludge without enzyme treatment.
Additionally still a chemical fusionprocess with NaOH had been carried out. After adding of the soda lye a rapid rising of the gas production was registered.
The separating of the process in two area parts, hydrolysis and methanogenesis, has well proved. Knowledge had been gained, that for the desired solid material degradation in the hydrolysis the dwell time is too short.
The incorporation of the stirrers into the pretreatment and in the post digestion brought the desired effect. By the better bacteria-substrate-contrast the capacity of the degradation has rised.
The selection of the lava slag as solid bed in the methanogenesis has not proved itself. Actually the bacteria growing was satisfactorily, but because of the thin and narrow passages and because of the high solid material charging it came to blockings in the area of the solid bed.
Furthermore it came to partial dissolving appearances, i.e. in the complete methanogenesis had been found lava sand. After standing phases the ultrafiltration membranes had been covered with a sludge and solid material film, which could be detached again only by a complete dismantling and mechanical cleaning of the module.
The solid/liquid separation between the hydrolysis and the methanogenesis could not be effected in the depositing vessel. The times for the sedimentation had been too long for the process procedure and float sludge forming counteracted the real aim.
In the post digestion the residue degradation of the carbon was too small, i.e. the odour molesting of the sludges had been too high. The filter press could not be operated in the provided manner, because by the bad digestion of the sludges in the post digestion a too high odour molesting arised at the filtrate and at the filter cake. The pressing off the filter cake was not effected in the desired manner, so that the working expenditure for the cleaning of the straining clothes had been much higher than originally planned.
The innovative treatment system consists of 4 consecutive steps. The slurry-type brewery waste will be enzymatically hydrolyzed to monomeric compounds, simultaneously fermented to organic acids and separately biomethanized. Preceeding these two steps is a buffer step to cope with the discontinuous fonctionning of the brewery, namely over the week-end. Following these two steps, is a step of physico-chemically-assisted thickening yielding a filtrate to be recycled in the 3rd step and a sludge to be composted.
The first step, buffering, takes place in 5 m3 tank where yeast and marc are mixed and heated at 70 deg.C. In this step, the Kieselghur filter aid is specifically removed by fast sedimentation, an essential part or the process.
In the second step, 220 l portions of the previous step are mixed with O.O1 % enzyme, heated at 70 deg.C and introduced in the first anaerobic reactor of next step.
The third step consists of 2 step biomethanation system : acidogenesis and methanogenesis. Acidogenesis is conducted in a 3step cascade mode with part of the sludge recycled, the excess sludge being led to step 4. The gas produced in the acidogenic step passes through the methanogenic reactor. The mixed liquor of the methanogenic step passes through an ultrafiltration device. The liquid portion is of good quality enough to be discharged in the sewer. The more solid portion is fed into step 4. The biogas is stored in a 15 m3 gasholder at low pressure and subsequently at 15 bar in a high pressure container of 67 m3 capacity, in order to allow for a 3 times a week use, at peak-demand times of energy in the brewery.
The fourth step collects the excess sludge, thickens it in a filterpress, recycles the filtrate in the third step and yields and easily compostable solid cake.
The waste to be treated amounts to 800 m3 y-1, containing 55,300 kg of TOC (total organic carbon).With an expected global conversion of 70%, the biogas yield is 72,000 Nm3 y-1,equivalent to 42.6 toe.
Total costs are 920,020 DM, all of it being eligible. EC contribution is
367,850 DM. Total investment cost is 678,020 DM. Maintenance and operation costs amount to 20,000 DM yearly. Per unit thermal kWh produced, this is equal respectively to 0.22 DM kWh -1 for investment cost and 0.04 DM kWh-1 for maintenance and operation costs. The energy saving, namely natural gas not bought amounts to 45 573 DM y -1. The fringe benefit for pollution abatement is estimated at 70 000 DM y-1.
The proposed solution is 8% more expensive (capital costs included) than the simple discharge of the waste and the purchase of an equivalent amount of natural gas. Nevertheless, the simple pay-back time, calculated on investment costs divided by the algebric sum of maintenance and operation costs, energy saving and pollution abatement fringe benefit (excluding capital costs) can be calculated equal to 7 years.
Monitoring includes mass balances around C (carbon), COD, P (phosphorus) and N (Nitrogen), biogas production
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
71085 Holzgerlingen
Germany