Conversion and toxicity characteristics of formaldehyde in acetoclastic methanogenic sludge

Operational Parameters of Biogas Plants: A Review and Evaluation Study

The biogas production technology has improved over the last years for the aim of reducing the costs of the process, increasing the biogas yields, and minimizing the greenhouse gas emissions. To obtain a stable and efficient biogas production, there are several design considerations and operational parameters to be taken into account. Besides, adapting the process to unanticipated conditions can be achieved by adequate monitoring of various operational parameters. This paper reviews the research that has been conducted over the last years. This review paper summarizes the developments in biogas design and operation, while highlighting the main factors that affect the efficiency of the anaerobic digestion process. The study’s outcomes revealed that the optimum operational values of the main parameters may vary from one biogas plant to another. Additionally, the negative conditions that should be avoided while operating a biogas plant were identified.

Biotreatability of wastewater generated during machinery washing in a wood-based industry: COD, formaldehyde and nitrogen removal

This paper describes biotreatability tests for treating a wastewater stream generated by wood-floor industries after cleaning and washing of machinery used to apply urea-formaldehyde resins onto wood-fiber boards. A biological system consisting of an anaerobic-intermittently aerated reactor in lab-scale was constructed. Since the investigated wastewater is intermittently generated, the system was designed to operate in batch mode. The treatment focused on removal of formaldehyde and COD, as well as the efficiency of nitrification-denitrification. The proposed cheap and relatively simple-to-operate biological system achieved COD and formaldehyde removal rates of 65+/-11% and 93+/-4% respectively. In spite of anaerobic ammonium removal and denitrification, the intermittently-aerated reactor showed poor performance for nitrification. Therefore, a better understanding of constraints for the process improvement is necessary. Regardless the constraints faced during the investigation, the proposed system can be considered feasible to partially reduce a great amount of biodegradable compounds in urea-formaldehyde-based wastewaters. However, to comply with strict threshold limits for industrial effluent discharges, the use of biological treatment combined with more advanced processes is needed to achieve a better quality of the final effluent.

Biomethanization of orange peel waste

Recent research has demonstrated that orange peel waste is a potentially valuable resource that can be developed into high value products such as methane. Following a pre-treatment to extract D-limonene, the anaerobic digestion of orange peel waste was evaluated at laboratory and pilot scale under mesophilic and thermophilic conditions. D-limonene removals of 70% were reached with pre-treatment. The results showed the convenience of thermophilic conditions for treating this waste as the methane production rate and biodegradability were higher than at mesophilic temperature. At pilot scale, a thermophilic continuously stirred-tank reactor working in semi-continuous mode was employed. The OLR was found to be in the range of 1.20-3.67 kg COD/m(3) d; the most appropriate range for working under stable conditions at SRT of 25 d. The methane yield coefficient was found to be 0.27-0.29 L(STP)CH(4)/g added COD and the biodegradability 84-90% under these conditions. However, acidification occurred at the highest OLR.

Degradation of formaldehyde in anaerobic sequencing batch biofilm reactor (ASBBR)

The present study evaluated the degradation of formaldehyde in a bench-scale anaerobic sequencing batch reactor, which contained biomass immobilized in polyurethane foam matrices. The reactor was operated for 212 days at 35 degrees C with 8h sequential cycles, under different affluent formaldehyde concentrations ranging from 31.6 to 1104.4 mg/L (formaldehyde loading rates from 0.08 to 2.78 kg/m(3)day). The results indicate excellent reactor stability and over 99% efficiency in formaldehyde removal, with average effluent formaldehyde concentration of 3.6+/-1.7 mg/L. Formaldehyde degradation rates increased from 204.9 to 698.3mg/Lh as the initial concentration of formaldehyde was increased from around 100 to around 1100 mg/L. However, accumulation of organic matter was observed in the effluent (chemical oxygen demand (COD) values above 500 mg/L) due to the presence of non-degraded organic acids, especially acetic and propionic acids. This observation poses an important question regarding the anaerobic route of formaldehyde degradation, which might differ substantially from that reported in the literature. The anaerobic degradation pathway can be associated with the formation of long-chain oligomers from formaldehyde. Such long- or short-chain polymers are probably the precursors of organic acid formation by means of acidogenic anaerobic microorganisms.

Use of electrochemical technology to increase the quality of the effluents of bio-oxidation processes. A case studied

In this work, it has been studied the use of conductive-diamond electrochemical oxidation (CDEO) as a refining technology to assure the quality of the effluents of door manufacturing processes (DMP). To do this, the raw effluents of these factories have been treated by a combination of physicochemical, biological and CDEO treatments. CDEO was found to be a feasible alternative to the refinement of a wooden DMP waste. It can successfully decrease the organic load of the effluents of the biological oxidation with low energy requirements. In addition, in case of incidents in the biological process, CDEO can treat successfully the effluents of the coagulation process. The effluents of the biological treatment have also been treated by CDEO in order to check the possible use of electrochemical technology to increase the biodegradability of the effluents and their possible recycle to the biological treatment. Unfortunately, electrochemical technology was found to be not adequate to increase the biodegradability of the effluents of a biological treatment. The hard oxidation conditions generated during CDEO do not lead to the accumulation of intermediates but to the almost direct formation of carbon dioxide. Lowering the current density or changing the electrodes can not enhance the biodegradability of the effluents of an electrochemical cell.