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FP5

AGROIWATECH Report Summary

Project ID: ICA2-CT-2002-10010
Funded under: FP5-INCO 2
Country: Bosnia and Herzegovina

Pilot scale data to design and operate agro-industrial wastes treatment plants

Anaerobic treatment technologies are used throughout the world for the effective treatment of municipal wastewaters and sludges as well as for the treatment of a wide variety of industrial wastewaters and organic solid wastes. This technology is particularly attractive in developing countries since the energy required for operating the process is minimal compared to the energy required for aerobic processes. In addition, energy for on-site use is produced in the form of methane gas, which can be converted to mechanical or electrical energy for local use. Moreover, effluent from anaerobic plants can have high fertilizing value and can be successfully used for land conditioning.

Solid wastes from agriculture, farming and food processing industries due to the high organic contents and biodegradability are good candidates for undergoes anaerobic degradation.

Unfortunately, the comparison of literature research data and drawing of conclusions is difficult because the diversity of reactor designs is matched by a large variability of the treated waste and choice of operational parameters (retention time, solids content, mixing, recirculation, inoculation, number of stages, temperature, ...).

Under this conditions there certainly does not exist a consensus over the optimal reactor design to treat agro-industry solid wastes. The reason most likely lies in the wide range of different waste sources, complexity of the biochemical pathways involved and the relative novelty of the technology.

The results presented contribute to asses the most promising technology for the anaerobic treatment of agro-industries solid wastes and, based on data obtained from the laboratory scale to provide data for process scale-up and operation at full scale. The chosen feedstock consist of wastes from the potato processing industry.
Moreover, the ADM1 model for anaerobic digestion has been validated and shown to be able to reproduce most of the measured parameters.

The experiments were carried out in tree different types of laboratory-scale reactors: conventional 5l CSTR reactor, inclined plug-flow reactor and a two-stages reactor consisting of two vessels operated in series, 6l acidogenic vessel with separation of solid and liquid phase and 6 l methanogenic vessel with variable useful volume depending on the amount and quality of liquid phase separated in the acidogenic reactor. The reactors were constructed of Plexiglas and placed in thermostatic chamber at 35oC together with gas measurement devices for each reactor.

All the reactors were equipped with a glass bottle for gas sampling just after gas cumulative volume measuring devices. Each sampling devices was protected from air intake by means of an hydraulic seal.

The reactors were fed once per day and five days per week thus the effective organic load has been calculated on a weekly average base. The performance of the reactor was tested in response to different loading rates (0.5-4.5g COD/L/day) and operational regimes.

Cumulative gas production has been recorded daily whereas characterization of the effluents has been normally performed weekly or every time was deemed interesting (i.e. change on organic load, gas production).

The Anaerobic Digestion Model 1 (implemented in the AQUASIM software for simulation of aquatic systems) has been adopted and after calibration using data from lab. scale reactors validated using preliminary data from a pilot scale inclined plug flow reactor.

Inclined plug flow reactor seems to be a good compromise between performances and simplicity of design and operation in treating agroindustrial wastes characterized by high biodegradability and high moisture content.

Its performances can be compared with Continuous-flow Stirred-Tank Reactors while whole plant design and operation are slightly easier.

Moreover, possibility that some settling occur in the upper part of the reactor can increase effluent quality in terms of suspended COD.

Mathematical model ADM1 prove to be able to simulate the process with a good accuracy. Further refining of the model could be able to predict overloading situations and to predict maximum achievable OLR.

From experimental data, operation at OLR up to 5 kgCOD/m3/d can be achieved. However, other problems than biological stability (i.e. foam) can be expected at high load (greater than 4.5 kg/COD/m3/d).

Contact

Tarik KUPUSOVIC, (Professor)
Tel.: +387-33-207949
Fax: +387-33-207949
E-mail
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