Worldwide, anaerobic digestion for sanitation and utilization of the produced biogas as energy carrier have a long-standing history. Concomitantly, digested residues from biogas plants are utilized as valuable fertilizers in crop production. In Germany, guaranteed prices for electricity generated from renewable sources pushed the number of biogas plants from about 140 in 1992 to about 7,720 by the end of 2013, and the share of electricity supply from biogas close to 4.5%. In the midterm, biogas is given considerable potential to fill up the residual load from electricity generation based on wind and photovoltaic. In this review, we give an overview of the state-of-the-art of biogas technology for energy supply from agricultural inputs, based mainly on the situation in Germany. Focus is placed on the monitoring and control (M&C) of biogas plants as a means of meeting the growing demands for productivity and reliability of biogas supply. We summarize prominent factors for the stability and productivity of the anaerobic digestion (AD) process, and present latest findings about molecular biology tools, bioindicators, the ‘metabolic quotient’ and cDNA/DNA ratios for process analysis. In view of the large diversity of agricultural biogas installations, we discuss the cost-benefit ratio of M&C effort and equipment. In the light of the transformation of the energy system in Germany towards renewable sources (‘Energiewende’), we give an outlook on prospects and concepts for the future role of biogas technology in agriculture and energy supply. We also address recent misguided developments, as the sustainable development of biogas technology in agriculture can only be realized within the ecological, economical, and social boundaries of underlying agro-ecological systems.

Grubbs test (extreme studentized deviate test, maximum normed residual test) is used in various fields to identify outliers in a data set, which are ranked in the order ofx1≤x2≤x3≤⋯≤xn (i=1,2,3,…,n). However, ranking of data eliminates the actual sequence of a data series, which is an important factor for determining outliers in some cases (e.g., time series). Thus in such a data set, Grubbs test will not identify outliers correctly. This paper introduces a technique for transforming data from sequence bound linear form to sequence unbound form(y=c). Applying Grubbs test to the new transformed data set detects outliers more accurately. In addition, the new technique improves the outlier detection capability of Grubbs test. Results show that, Grubbs test was capable of identifing outliers at significance level 0.01 after transformation, while it was unable to identify those prior to transforming at significance level 0.05.

We evaluated quantitative real-time PCR (qPCR) and RTqPCR (for RNA species) for their ability to quantify microorganisms and viruses in problematic environmental samples such as cattle manure, digester material, wastewater and soil. Important developments included a standard spiking approach which compensated for methodological bias and allowed sample-to-sample comparison and reliable quantification. Programme CeTe was developed to calculate endogenous concentrations of target organisms (nucleic acid copies) for each sample separately from the generated standard curves. The approach also permitted assessment of the detection limit of the complete method, including extraction. It varied from sample to sample, due to different extraction efficiencies and variable co-extraction of PCR inhibitors. False negative results were thereby avoided. By using this approach we were able to optimise a DNA extraction protocol from the different tested sample types. Protocols for the extraction of RNA species from environmental samples were also optimised. DNA was (almost) not degraded after lethal shock (autoclaving) in the sterile environment. In contrast, the parallel selective cultivation and qPCR results for various microbial parameters from an anaerobic digester chain suggested that DNA from decaying organisms was readily recycled in metabolically active environments. It may, therefore, be used to determine viable organisms in samples exhibiting substantial metabolic turnover. It is proposed that our standard spiking approach, including data evaluation by the program CeTe, should be considered in future standardisation and norms for the quantification of nucleic acid containing organisms in environmental and product samples.