**2.3 The experimental setup**

We performed the examination of the effects of the seeding material on the dry batch anaerobic treatment by a series of reactors of a total capacity of 6 dm3, which consisted of 4 reactors, each of a capacity of 1.5 dm3, connected in parallel. By these set ups, the disturbing effects (opening of reactors) occurring during the pH measurements were reduced (Figure 2). The reactors were connected to gas-collecting bags.

Fig. 2. Set of dry batch anaerobic reactors

As experimental variable we checked five different seeding material ratios. We set the organic waste to seeding material ratios projected to the quantity of dry organic material, to these values: 1:0.5; 1:1; 1:1.5; 1:2, and 1:3. We measured the gas production of the seeding material (digested sludge) in a control reactor, thus, the degradation rate of the biowaste could be calculated separately. We compared the treatments when the sewage sludge is treated alone and when is co-digested with VFG waste, with the 1:1 seeding material ratio usually applied in the practice for the anaerobic treatment of municipal organic wastes. We kept the reactors in a room of a constant temperature of 34°C.

To determine the methanogenic activity of the seeding material we used neutralized acetic acid as a substrate. To decrease the retardatory effects we added macro- and micro-nutrients (Biotechnion, 1996), and incubated the samples on the temperature of 35°C. We used liquidphased mixed reactors to decrease the substrate-gradient. The amount of biogas generated, was calculated on the basis of pressure changes in the head-part of the 1.5 dm3 reactors. To remove the generated CO2, NaOH pellets were placed in the heads-part of the reactors. Specific methanogenic activity of the seed was calculated on the basis of cumulative

The acidity of the sludge was checked by a pH meter (340i WTW) pH/mV measuring

We performed the examination of the effects of the seeding material on the dry batch anaerobic treatment by a series of reactors of a total capacity of 6 dm3, which consisted of 4 reactors, each of a capacity of 1.5 dm3, connected in parallel. By these set ups, the disturbing effects (opening of reactors) occurring during the pH measurements were reduced (Figure

As experimental variable we checked five different seeding material ratios. We set the organic waste to seeding material ratios projected to the quantity of dry organic material, to these values: 1:0.5; 1:1; 1:1.5; 1:2, and 1:3. We measured the gas production of the seeding material (digested sludge) in a control reactor, thus, the degradation rate of the biowaste could be calculated separately. We compared the treatments when the sewage sludge is treated alone and when is co-digested with VFG waste, with the 1:1 seeding material ratio usually applied in the practice for the anaerobic treatment of municipal organic wastes. We

methane production graphs by taking the tangent of the deepest slope of the curve.

device, to which a SenTix 41 type electrode was connected.

2). The reactors were connected to gas-collecting bags.

Fig. 2. Set of dry batch anaerobic reactors

kept the reactors in a room of a constant temperature of 34°C.

**2.3 The experimental setup** 
