Research Literature Review

Most reviews of anaerobic digestion research tell you what works. This one tells you how well anyone actually knows that.

Thirty-two developments are set out in a single consistent format - theme, maturity, evidence base, then finding, mechanism, practical reading and caveat — so that a full-scale intervention with a decade of operating history can be compared directly against a promising result from a bench-scale bottle test. The grading is the point: the evidence pyramid in this field is very broad at laboratory level and very narrow above it, and a great deal of enthusiasm rests on work that has never run continuously at scale.

Coverage runs across seven parts. Additives, including conductive carbon and direct interspecies electron transfer, biochar property control, iron composites, trace elements and nanobubbles. Pretreatment, where combined methods consistently beat single ones. Reactor engineering, from CFD-led mixing design to membrane bioreactors and micro-aeration. Electrochemical and gas-phase intensification, covering microbial electrolysis and both in-situ and ex-situ biomethanation. Microbiology, process control and machine learning. And digestate valorisation.

A closing synthesis separates what the literature broadly agrees on from what remains genuinely contested, sets out four structural problems with the evidence base - the scale distribution, missing energy balances, control selection inflating headline percentages, and publication bias toward yield over resilience - and identifies research gaps with clear commercial pull.

33 pages, 65 references. Volume One of the Technical Review Series.