ISO/NP 27092

Biogas — Determination of methane production and production rate from anaerobic digestate and process materials by real-time volumetric measurement

Scope

This document specifies a measurement method for the real-time volumetric quantification of methane production and production rate from organic materials under controlled anaerobic digestion conditions. Carbon dioxide and hydrogen sulfide are selectively removed using an alkaline absorption solution, and ammonia is selectively removed using an acidic absorption solution, both installed upstream of the gas-measurement device, so that the residual methane can be quantified continuously by volumetric measurement.
This document specifies two assessment modes. In the digestate assessment mode, digestate collected from an operating anaerobic digestion facility is used as the test material in its as-received condition, without inoculum standardisation, to determine the residual methane production and production rate of that facility's digestate. In the added-material assessment mode, digestate is used as the inoculum and a separate organic test material is added, with the methane production attributable to the added material determined by subtracting an inoculum blank. Unlike existing endpoint biogas-yield methods that determine a single, inoculum-independent value at the conclusion of an incubation period, this document provides continuous, time-resolved methane production and production-rate data for the material or digestate under test.
The method is applicable to organic materials compatible with anaerobic digestion, including but not limited to:
— agricultural residues, energy crops, livestock and food waste, sewage sludge, and municipal or industrial organic waste;
— biodegradable plastic materials, bioplastics and polymeric materials (e.g. PLA, PHA, PBAT blends) intended for anaerobic digestion or co-digestion; and
— digestate collected from operating anaerobic digestion facilities, assessed using its own as-received microbial community.
The test temperature may represent mesophilic (typically 35 °C to 40 °C) or thermophilic (typically 50 °C to 57 °C) anaerobic digestion; these ranges are given for information only, and the test temperature is determined by the operating temperature of the source facility or by the test plan. Methane production is monitored by real-time or short-interval volumetric measurement, and the test is terminated when the cumulative methane production curve reaches a predefined plateau or after a measurement period specified in the test plan.
This document is limited to the instrumental measurement of methane production and production rate. It does not determine ultimate anaerobic biodegradability or a percentage conversion of organic carbon into methane and carbon dioxide, and it does not determine an inoculum-independent, standardised value representing the maximum theoretical methane yield of a substrate; such determinations are addressed by ISO 11734 and by other ISO/TC 255 deliverables concerned with substrate characterisation. Results obtained by this document are specific to the identified facility or test material and to the condition of the digestate at the time of sampling.