Dajana Kučić

Biodegradation of tobacco waste by composting: Genetic identification of nicotine-degrading bacteria and kinetic analysis of transformations in leachate

The tobacco industry produces large quantities of solid and liquid waste. This waste poses a significant environmental problem, as some major components are harmful and toxic. The aim of this work is to isolate and identify the nicotine-degrading microorganisms in the composting of tobacco waste. The bioremediation process for the detoxification of waste was carried out in a column reactor at an airflow-rate of 0.4 L min−1 kg−1. The concentrations of nicotine and number of CFU in the samples taken from reactor were monitored over nineteen days. After nineteen days, 89.8 % of nicotine conversion was obtained. A nicotine-degrading bacterium, strain FN, was isolated from the composting mass and identified as Pseudomonas aeruginosa on the basis of morphology, 16S rDNA sequence, and the phylogenetic characteristics. To confirm that the isolated Pseudomonas aeruginosa FN is the actual nicotine degrader, batch experiments were performed using tobacco leachate. It was confirmed that the strain FN possesses a considerable capacity to degrade nicotine with simultaneous COD removal. The Monod kinetic model for single substrate was applied to obtain the substrate degradation rate and half saturation constant.

Zeolite and potting soil sorption of CO2 and NH3 evolved during co-composting of grape and tobacco waste

The gaseous byproducts produced during the composting of different kinds of solid waste are carbon dioxide (CO2) and ammonia (NH3). CO2 is a greenhouse gas and NH3 is a toxic and corrosive air pollutant so, they must be removed from exhaust gases prior to release into the atmosphere. The purpose of this work was to investigate the sorption of CO2 and NH3, evolved during composting, on zeolite and potting soil. The composting of the mixture of grape waste (GW) and tobacco waste (TW) in the mass ratio GW: TW = 55: 45 (dry mass basis) was carried out under forced aeration (0.645 L min−1 kg−1) in a column reactor (10 L) under adiabatic conditions over 21 days. Adsorption of the gases evolved was carried out in the fixed-bed column reactor (0.166 L). The most important physical-chemical characteristics of the composting mass and adsorbents and the evolved CO2 and NH3 were closely monitored. The highest CO2 and NH3 concentrations were measured at the thermophilic stage and the cooling stage of composting, respectively. The results showed that zeolite and potting soil were good adsorbents for the sorption of CO2 and NH3. The zeolite adsorbed 31 % of the evolved CO2 and the entire concentration of ammonia, whilst the potting soil adsorbed 3 % of CO2 and 49 % of NH3 from the exhaust gases.

Biodegradation of Agro-industrial Waste

The production of agro-industrial waste is growing worldwide and these wastes cannot be disposed on the ground without treatment. The objective of this work was to conduct composting process and anaerobic digestion of a mixture of agro-industrial waste (W), grape (GW), olive (OW) and tobacco (TW) waste. The composting process and anaerobic digestion of the mixture of GW, OW and TW in the ratio GW:OW:TW = 1:1:1.98 (dry matter) were carried out in column reactors with effective volume of 10 dm3 and 124 cm3, respectively, during 21 days. The composting experiment was carried out under forced aeration, while anaerobic digestion was conducted without aeration at temperature of 37 °C in anaerobic digester. Three different anaerobic experiments were conducted, without inoculum (E1) and with different ratio of inoculum and waste (E2, E3). During 21 days of composting of agro-industrial waste, the obtained conversion was 50 %. The volume of biogas produced during 21 days in experiments E1, E2 and E3 was 256 cm3, 280 cm3 and 162 cm3, respectively.

Emission of Gases During Composting of Solid Waste

Composting is a biochemical process converting organic components into stable compost with release of heat, water, CO2 and NH3. The objective of this work was to determine the amount of CO2 and NH3 in the exhaust gases during composting of tobacco waste (TW) and mixture of tobacco and grape waste (TGW). The cumulative evolved CO2 during 21 days of composting of TW and TGW, per mass of volatile matter, was 94.01 g kg−1 and 208.18 g kg−1, respectively, and cumulative evolved NH3 during composting of TW and TGW, per mass of volatile matter, was 504.81 mg kg−1 and 122.45 mg kg−1, respectively.