An interlaboratory study as useful tool for proficiency testing of chemical oxygen demand measurements using solid substrates and liquid samples with high suspended solid content

Determination of chemical oxygen demand of agricultural wastes by combining acid hydrolysis and commercial COD kit analysis

Chemical oxygen demand (COD) is an essential parameter in waste management, particularly for monitoring bioprocess such as anaerobic digestion. Indeed, chemical oxygen demand (COD) is a key parameter that can prove useful for the evaluation of waste biodegradability and to evaluate mass and energetic balances of the overall process. In this study, an adapted method to determine the COD of solid agricultural wastes was developed. This method combined a double acid hydrolysis of the solid waste materials followed by commercial COD tubes analysis. This method was compared to direct sampling after a standard dilution (3.5 g TS.L^-1) and analysis in commercial COD tubes. The method developed in this study allowed the COD of nine agricultural wastes to be accurately predicted, with an absolute error of 7% compared to the theoretical COD. In comparison, the method with only a prior water dilution resulted in higher absolute errors of 36% and 31% when sampling was performed with pipette tips and cut pipette tips, respectively.

Biochemical Methane Potential (BMP) Assay Method for Anaerobic Digestion Research

Biochemical methane potential (BMP) tests are widely used for characterizing a substrate’s influence on the anaerobic digestion process. As of 2018, there continues to be a lack of standardization of units and techniques, which impacts the comparability and validity of BMP results. However, BMP methods continue to evolve, and key aspects are studied to further eliminate systematic errors. This paper aims to update these key aspects with the latest research progress both to introduce the importance of each variable to those new to BMP measurements and to show the complexity required to design an accurate BMP test.

Solid anaerobic digestion: State-of-art, scientific and technological hurdles

In this paper, a state-of-art about solid anaerobic digestion (AD), focused on recent progress and trends of research is proposed. Solid anaerobic digestion should be the most appropriate process for degradation of by-products with high total solid (TS) content, especially lignocellulosic materials like agricultural waste (straw, manure), household waste and food waste. Solid AD is already widely used in waste water treatment plant for treating plant for sewage sludge but could be more developed for lignocellulosic materials with high TS content. Many research works were carried out in Europe on solid AD, focused on current hurdles (BMP, codigestion, inhibition, microbial population, rheology, water transfers, inoculum, etc.) in order to optimize the solid AD process. In conclusion, hurdles of solid AD process should and must be solved in order to propose better productivity and profitability of such system operating with high TS content (>15%), favouring reliable industrial processes.

Performance evaluation of the bioreactor landfill in treatment and stabilisation of mechanically biologically treated municipal solid waste

The potential of bioreactor landfills to treat mechanically biologically treated municipal solid waste is analysed in this study. Developing countries like India and China have begun to investigate bioreactor landfills for municipal solid waste management. This article describes the impacts of leachate recirculation on waste stabilisation, landfill gas generation, leachate characteristics and long-term waste settlement. A small-scale and large-scale anaerobic cell were filled with mechanically biologically treated municipal solid waste collected from a landfill site at the outskirts of Bangalore, India. Leachate collected from the same landfill site was recirculated at the rate of 2-5 times a month on a regular basis for 370 days. The total quantity of gas generated was around 416 L in the large-scale reactor and 21 L in the small-scale reactor, respectively. Differential settlements ranging from 20%-26% were observed at two different locations in the large reactor, whereas 30% of settlement was observed in the small reactor. The biological oxygen demand/chemical oxygen demand (COD) ratio indicated that the waste in the large reactor was stabilised at the end of 1 year. The performance of the bioreactor with respect to the reactor size, temperature, landfill gas and leachate quality was analysed and it was found that the bioreactor landfill is efficient in the treatment and stabilising of mechanically biologically treated municipal solid waste.

Towards a standardization of biomethane potential tests

Production of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. Although several norms and guidelines for BMP tests exist, inter-laboratory tests regularly show high variability of BMPs for the same substrate. A workshop was held in June 2015, in Leysin, Switzerland, with over 40 attendees from 30 laboratories around the world, to agree on common solutions to the conundrum of inconsistent BMP test results. This paper presents the consensus of the intense roundtable discussions and cross-comparison of methodologies used in respective laboratories. Compulsory elements for the validation of BMP results were defined. They include the minimal number of replicates, the request to carry out blank and positive control assays, a criterion for the test duration, details on BMP calculation, and last but not least criteria for rejection of the BMP tests. Finally, recommendations on items that strongly influence the outcome of BMP tests such as inoculum characteristics, substrate preparation, test setup, and data analysis are presented to increase the probability of obtaining validated and reproducible results.

A modified method for COD determination of solid waste, using a commercial COD kit and an adapted disposable weighing support

The chemical oxygen demand (COD) is an essential parameter in waste management, particularly when monitoring wet anaerobic digestion processes. An adapted method to determine COD was developed for solid waste (total solids >15%). This method used commercial COD tubes and did not require sample dilution. A homemade plastic weighing support was used to transfer the solid sample into COD tubes. Potassium hydrogen phthalate and glucose used as standards showed an excellent repeatability. A small underestimation of the theoretical COD value (standard values around 5% lower than theoretical values) was also observed, mainly due to the intrinsic COD of the weighing support and to measurement uncertainties. The adapted COD method was tested using various solid wastes in the range of 1-8 mg_COD, determining the COD of dried and ground cellulose, cattle manure, straw and a mixed-substrate sample. This new adapted method could be used to monitor and design dry anaerobic digestion processes.

Determination of chemical oxygen demand in heterogeneous solid or semisolid samples using a novel method combining solid dilutions as a preparation step followed by optimized closed reflux and colorimetric measurement

This paper reports the development of an innovative sample preparation method for the determination of the chemical oxygen demand (COD) in heterogeneous solid or semisolid samples, with high suspended solids and COD concentrations, using an optimized closed reflux colorimetric method. The novel method, named solid dilution (SD), is based on a different technique of sample preparation, diluting the sample with magnesium sulfate (MgSO(4)) previous to COD determination. With this, it is possible to obtain a solid homogeneous mixture much more easily analyzable. Besides, a modification of concentration and ratio of reagents was optimized to make the closed reflux colorimetric method suitable for complex substrates with COD levels ranging from 5 to 2500 g O(2) kg(-1) TS. The optimized method has been tested with potassium hydrogen phthalate (KHP) as primary solid standard and using different solid or semiliquid substrates like pig slaughterhouse waste and sewage sludge, among others. Finally, the optimized method (SD/SM-CRC) was intensively tested in comparison to the standard titrimetric method (SM-ORT) using different certified reference materials (CRM). The developed method was found to give higher accuracy, 1.4% relative standard deviation (RSD) vs 10.4%, and bias of 2.8% vs 8.0%, in comparison to the standard open reflux titrimetric method.