Pyrolysis of domestic sewage sludge: influence of operational conditions on the product yields using factorial design.

This study aims to investigate a sustainable method for sewage sludge (SS) safe disposal and reuse. The study involved exploring the optimum parameters of thermal treatment of SS by pyrolysis to produce biochar. Based on the analysis of the full factorial design, the effects of pyrolysis conditions: temperature, heating rate, and isothermal time on pyrolysis product yields were evaluated. The average yield of biochar was significantly reduced when the pyrolysis temperature was increased from 300 to 500 °C, while the average yields of bio-oil (BO) and non-condensable gases (NCGs) were increased. The yield of biochar was nearly the same when the heating rate was increased from 5 to 35 °C/min, while the yield of BO was increased and the yield of NCGs was decreased. The average yields of biochar and NCGs were reduced when the isothermal time was increased from 45 to 120 min, while the yield of BO was slightly increased. Factorial design methodology revealed all potential interactions between the variables of the pyrolysis process of SS. To predict pyrolysis product yields, first-order regression models were developed based on the effects' magnitude of the process parameters and their interactions. The models were agreed to the experimental data.

Selection of bacteria and plant seeds for potential use in the remediation of diesel contaminated soils.

Enumeration and recovery of the dominant bacteria from a chronically fuel contaminated soil has been investigated. Bacterial counts from these polluted soils ranged between 0.70x10(8) and 28.20x10(8) CFU/g soil. Three different types of bacterial colonies have been recovered on the agar plates. Biochemical examination of the recovered bacteria revealed that they mainly belonged to the genus Pseudomonas, Micrococcus and Bacillus. Turbidity, cell biomass (dry weight basis), and physical appearance determined the growth of these bacteria on diesel. A noticeable decline in alfalfa (Medicago sativa) seeds germination of 15-30% was shown at 500 mg/kg diesel or higher. Under these contaminated conditions, fescue grass (Cyndon dactylon) exhibited a higher viability than alfalfa indicating that C. dactylon seeds are relatively tolerant to diesel and can possibly be used in phytoremediation of diesel contaminated soils. Results of diesel phyotoxicity to seed germination of these two plants were based on filter paper media and therefore; should be considered as first indication only. Extrapolation of such results to actual soil conditions should be cautiously approached taking into account diesel sorption on soil and mechanisms of its bioavailability.