Main characteristics of tobacco waste generated during the processing of tobacco for cigarette manufacture are a high content of nicotine and total organic C. Composting is a way for decreasing the levels of nicotine and total organic C in tobacco waste and for disposal of this kind of agro-industrial waste. Changes in pH and electrical conductivity and activities of dehydrogenase, protease, alkaline phosphatase and β-glucosidase were determined during composting of tobacco waste (TW) and mixtures of TW + grape pomace (GP) and TW + olive pomace (OP). The nicotine in the tobacco waste was completely decomposed by composting. In the final composts, total organic C content and C : N ratio decreased, whereas the contents of total N, P and K increased. The pH of the composts increased rapidly at first and then more slowly and the electrical conductivity first decreased and then increased during composting. Mixing the tobacco waste with the other compost materials decreased the electrical conductivity level by 32 and 46% in the final TW + GP and TW + OP composts, respectively. The highest activities of the studied enzymes were observed on the third week of the composting process for dehydrogenase, the fifth week for protease and β-glucosidase and the ninth week for alkaline phosphatase. All enzyme activities stabilized about in 4 months.

Conventional parameters (loss on ignition, total organic carbon, total nitrogen, C/N-ratio, respiration activity (RA₄), compost status (= ‘Rottegrad’), NH₄-N and NO₃-N) are not correlated to humification. At best, they provide information on the biological stability (status of degradation) of composts. Humic substances which are a source of stable organic matter and nutrients are discussed as a parameter describing compost quality. Thus, in the present research project a photometric method evaluating humic acids was used to characterize the quality of 211 Austrian and foreign composts made from source-separated collected biowaste or sewage sludge. Furthermore, parameters influencing the formation of humic acids during the rotting process were investigated by implementing rotting experiments in the laboratory as well as in composting plants. The analysed composts showed humic acid contents between 2.5 and 47 %, calculated on a organic dry matter (oDM) basis. In addition to the duration of treatment the main influence on humification was the feedstock used. Stabilized sewage sludge, biowaste after intensive anaerobic pre-treatment or biowaste with low reactivity (RA₄) or uniform composition (e.g. mainly grass) showed a low formation of humic acids. For optimum humification the feedstock needed to contain components that are well balanced from scarcely to easily degradable compounds. Processing also influenced humification. Open windrow systems and reactor systems allow the same quality to be produced when operated well, but optimizing mineralization (e.g. very intensive aeration) showed negative effects. The positive condition required for humification is an unhurried (not too intense) degradation with long-lasting biological activity in which microbes have enough time to use the metabolic products of degradation for humification.

The present study investigated the development of high sugar production by optimization of an enzymatic hydrolysis process using both conventional and statistical methods, as well as the production of ethanol by the selected wastepaper source. Among four sources of pretreated wastepaper including office paper, newspaper, handbills and cardboard, office paper gave the highest values of cellulose (87.12%) and holocelluloses (89.07%). The effects of the amount of wastepaper, the pretreatment method and the type of enzyme on reducing sugar production from office paper were studied using conventional methods. The highest reducing sugar production (1851.28 µg L^–1; 37.03% conversion of glucose) was obtained from the optimal condition containing 40 mg of office paper, pretreated with stream explosion and hydrolysed with the combination of cellulase from Aspergillus niger and Trichoderma viride at the fixed loading rate of 20 FPU g^–1 sample. The effects of interaction of wastepaper amount and enzyme concentration as well as incubation time were studied by a statistical method using central composite design. The optimal medium composition consisted of 43.97 µg L^–1, 28.14 FPU g^–1 sample and 53.73 h of wastepaper, enzyme concentration and incubation time, respectively, and gave the highest amount of sugar production (2184.22 µg L^–1) and percentage conversion of glucose (43.68%). The ethanol production from pretreated office paper using Saccharomyces cerevisiae in a simultaneous saccharification and fermentation process was 21.02 g L^–1 after 36 h of cultivation, corresponding to an ethanol volumetric production rate of 0.58 g ethanol L^–1 h^–1.