The yearly variations of the quality of the upgraded biogas and the efficiency of digestate treatment were evaluated in an outdoors pilot scale high rate algal pond (HRAP) interconnected to an external absorption column (AC) via a conical settler. CO concentrations in the upgraded biogas ranged from 0.7% in August to 11.9% in December, while a complete HS removal was achieved regardless of the operational month. CH concentrations ranged from 85.2% in December to 97.9% in June, with a limited O and N stripping in the upgraded biogas mediated by the low recycling liquid/biogas ratio in the AC. Biomass productivity ranged from 0.0 g m d in winter to 22.5 g m d in summer. Finally, microalgae diversity was severely reduced throughout the year likely due to the increasing salinity in the cultivation broth of the HRAP induced by process operation in the absence of effluent.

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12The influence of the daily and seasonal variations of environmental conditions on the 13 quality of the upgraded biogas was evaluated in an outdoors pilot scale high rate algal

The transformation of CH 4 -rich biogas into poly-(hydroxyalkanoates) (PHAs) using methanotrophic bacteria has recently emerged as an attractive and worldwide applicable alternative to its current use as an energy source. The influence of the geographical location on the economic performance of combined heat and electricity production (CHP) and/or PHA production from biogas generated in waste treatment plants was evaluated in 13 representative regions of the world. In addition, the sensitivity of PHA production costs toward current biotechnological limitations and commodity prices was evaluated. The geographical analysis showed a high net present value (NPV 20 ) variability around the world (from −7.17 to +16.27 M€). Countries with the lowest NPV 20 also exhibited the lowest PHA production costs (4.1 €•kg −1 PHA), which suggested that biopolymer production represents an alternative biogas valorization pathway in regions where CHP is not economically viable. In countries with high energy prices, the use of biogas surplus from anaerobic waste treatment for PHA production enhanced the economic performance and mitigated the electric market dependence of current CHP plants. CH 4 elimination capacity in bioreactors and PHA accumulation yield in bacterial cells were identified as the main biotechnological bottlenecks toward production of biopolymers competitive in price (0.2−1.7 €•kg −1 PHA) with their oil-based counterparts.