The discovery story of photovoltaic cells is entirely typical. Chance played a role in it, and before it went to the average user, it first served the army. In addition, as with the discovery of electricity, there are many scientists and more than 100 years of technological development behind how modern photovoltaic cells and solar panels work. The first photovoltaic panels were able to power, at most, a radio. Today their power allows for the production of energy for the entire household. Technology is continuously developing, and the hence achieved efficiency keeps growing. Modern silicon solar cells of large photovoltaic farms power thousands of buildings, and this installation can be seen more and more often. This article describes the development of the use of solar energy since ancient times and the comprehensive history of the invention of the photovoltaic cell, starting with the discovery of the photoelectric effect by Edmond Becquerel in 1839 to the achievement of nearly 50% efficiency under laboratory conditions. The advances in photovoltaic cell efficiency and the price of energy production per watt over the years are also shown. Examples of the first applications of photovoltaics are given, and profiles of figures who contributed to the development of solar technology are introduced. The considerable influence of Polish scientists on the development of the photovoltaic cell is also highlighted. Without them, this method of obtaining energy would perhaps not be at high levelh level today.

Anaerobic digestion is an important technology for the bio-based economy. The stability of the process is crucial for its successful implementation and depends on the structure and functional stability of the microbial community. In this study, the total microbial community was analyzed during mesophilic fermentation of sewage sludge in full-scale digesters.

The digesters operated at 34–35°C, and a mixture of primary and excess sludge at a ratio of 2:1 was added to the digesters at 550 m3/d, for a sludge load of 0.054 m3/(m3·d). The amount and composition of biogas were determined. The microbial structure of the biomass from the digesters was investigated with use of next-generation sequencing.

The percentage of methanogens in the biomass reached 21%, resulting in high quality biogas (over 61% methane content). The abundance of syntrophic bacteria was 4.47%, and stable methane production occurred at a Methanomicrobia to Synergistia ratio of 4.6:1.0. The two most numerous genera of methanogens (about 11% total) were Methanosaeta and Methanolinea, indicating that, at the low substrate loading in the digester, the acetoclastic and hydrogenotrophic paths of methane production were equally important. The high abundance of the order Bacteroidetes, including the class Cytophagia (11.6% of all sequences), indicated the high potential of the biomass for efficient degradation of lignocellulitic substances, and for degradation of protein and amino acids to acetate and ammonia.

This study sheds light on the ecology of microbial groups that are involved in mesophilic fermentation in mature, stably-performing microbiota in full-scale reactors fed with sewage sludge under low substrate loading.

The elemental composition and morphology of aerobic granules in sequencing batch reactors (GSBRs) treating high-nitrogen digester supernatant was investigated. The investigation particularly focused on the effect of the number of anoxic phases (one vs. two) in the cycle and the dose of external organics loading (450 mg COD/(L·cycle) vs. 540 mg COD/(L·cycle)) on granule characteristics. Granules in all reactors were formed of many single cells of rod and spherical bacteria. Addition of the second anoxic phase in the GSBR cycle resulted in enhanced settling properties of the granules of about 10.6% and at the same time decreased granule diameter of about 19.4%. The study showed that external organics loading was the deciding factor in the elemental composition of biomass. At 540 mg COD/(L·cycle) the granules contained more weight% of C, S and N, suggesting more volatile material in the granule structure. At lower organics loadings granules had the higher diameter of granules which limited the diffusion of oxygen and favored precipitation of mineral compounds in the granule interior. In this biomass higher content of Mg, P and Ca, was observed.