A gas sensor array consisting of eight metal oxide semiconductor (MOS) type gas sensors was evaluated for its ability for assessment of the selected wastewater parameters. Municipal wastewater was collected in a wastewater treatment plant (WWTP) in a primary sedimentation tank and was treated in a laboratory-scale sequential batch reactor (SBR). A comparison of the gas sensor array (electronic nose) response to the standard physical-chemical parameters of treated wastewater was performed. To analyze the measurement results, artificial neural networks were used. E-nose—gas sensors array and artificial neural networks proved to be a suitable method for the monitoring of treated wastewater quality. Neural networks used for data validation showed high correlation between the electronic nose readouts and: (I) chemical oxygen demand (COD) (r = 0.988); (II) total suspended solids (TSS) (r = 0.938); (III) turbidity (r = 0.940); (IV) pH (r = 0.554); (V) nitrogen compounds: N-NO₃ (r = 0.958), N-NO₂ (r = 0.869) and N-NH₃ (r = 0.978); (VI) and volatile organic compounds (VOC) (r = 0.987). Good correlation of the abovementioned parameters are observed under stable treatment conditions in a laboratory batch reactor.

The possibility of distinguishing different soil moisture levels by electronic nose (e-nose) was studied. Ten arable soils of various types were investigated. The measurements were performed for air-dry (AD) soils stored for one year, then moistened to field water capacity and finally dried within a period of 180 days. The volatile fingerprints changed during the course of drying. At the end of the drying cycle, the fingerprints were similar to those of the initial AD soils. Principal component analysis (PCA) and artificial neural network (ANN) analysis showed that e-nose results can be used to distinguish soil moisture. It was also shown that different soils can give different e-nose signals at the same moistures.

Contamination of soil with petroleum products is a major environmental problem. Therefore, one of the issues related to environmental protection is assessment of the ability of soil microbial populations to biodegrade petroleum-derived substances. The aim of the study was to compare the dynamics and fractionation of carbon isotopes during biodegradation of selected petroleum products (petrol and diesel) in soil characterised by optimal humidity for plants. The analyses were performed on soil material sampled from the arable layer of a fertile soil (chernozem) in central Poland. The soil samples were treated with two petroleum substances, i.e. unleaded 95-octane petrol and diesel fuel. The dynamics of changes was assessed by monitoring carbon dioxide content and oxygen content in the headspace over the soil surface. Additionally, the ratio of δ¹³C carbon isotopes was measured in the substrates added (petrol and diesel) and in CO₂ emitted to the atmosphere. In summary, it should be concluded that the rate of biodegradation of petrol was higher than that of diesel fuel. In the case of petrol, the process of stabilisation of the CO₂ concentration over the soil surface was completed within several days, whereas in diesel the process lasted at least a few weeks. The Isotope Ratio Mass Spectrometry technique and analysis of changes in δ¹³C in the samples indicated selective biodegradation of hydrocarbons contained in petrol and diesel fuel. Lighter fractions (constituting a greater proportion in petrol than in diesel) are metabolised more readily than heavier fractions.

The protists notably ciliates and testate amoebas in the conditions of modernized wastewater treatment plants “Hajdow” (Lublin, Poland) and the nitrogen removal efficiency were studied. Sampling took place every week during the period of August-September 2010. The total of 31 taxa of ciliates and 3 taxa of testate amoebas were identified. Most of the species were registered during the whole research period. Significant abundance reached the following species: Acineria uncinata, Aspidisca cicada, Aspidisca lynceus, Vorticella aquadulcis, Vorticella infusionum, Arcella vulgaris, Euglypha acanthophora and Pyxidicula operculata. In September increase in efficiency of nitrogen removal process was registered. The research shows that the increase of nitrogen reduction efficiency was accompanied by increase of ciliates quantity, mainly due to peritrichid ciliates.

Laboratory-scale sequencing batch reactors (SBR) with activated sludge were used for co-treatment of drilling mud and municipal wastewater. The influence of two doses of drilling mud, 1% (SBR2) and 3% (SBR3) of total added wastewater volume, on wastewater treatment efficiency and community of eukaryotes in activated sludge was examined. Addition of drilling mud significantly decreased the efficiency of TSS removal in SBR2 and SBR3 (from 97% in control bioreactor SBR1 to 75% and 49%, respectively), COD removal (from 93% to 57% and 48%, respectively) and removal (from 93% to 56% and 48%, respectively). Values of TSS concentration in outflow from SBR2 and SBR3 greatly exceeded the limit value appointed for the wastewater discharged into the environment. Drilling mud addition led to decrease in population and diversity of eukaryotes’ groups in activated sludge, which was reflected by changes in sludge biotic index (SBI). It amounted to 10 in all the SBRs at the beginning of the experiment, and in SBR1, it remained at this same high level throughout. After 1% addition of drilling mud, a slight decrease in SBI (to 8) was observed, but 3% addition lowered the SBI to 4, reflecting serious deterioration of activated sludge quality.