Volume 29 (2022): Issue 1 (March 2022)

In this study, nanoiron and nanoiron+Au particles were synthesised using aqueous Aegle marmelos extract using a facile and one-pot approach. Lower size non-magnetic nanoiron (~34 nm) and nanoiron (~34 nm) +Au particles (1 to 1.5 µm) were produced from the same medium individually. Nanoparticles suspension behaviour and structural characterisations were carried out by UV-Vis spectroscopy, electron microscopy and by X-ray diffraction techniques. Primarily, for synthesis, a simple bioreduction approach generated amorphous nanoiron particles, which on annealing produced magnetic maghemite, γ-Fe₂O₃ type nanoparticles with sizes 100 to 1000 nm. Posteriorly, the bioreduction process also produces nanoiron+Au particles and can be used for multifunctional applications. As a model application, catalytic application of the as-prepared nanoiron and nanoiron+Au particles towards methylene blue, a thiazine dye degradation is investigated and found to be effective within 20 min. Langmuir-Hinshelwood kinetic model was exploited to know the degradation behaviour, and the model was found to be fit based on R² values with the observed experimental data. We suggest that the formed highly stable nanoiron particles with in situ stabilisation offer benefits like consistency, environmental friendliness and suits well for large-scale applicability.

Wood wastes are one of the leading contributors of greenhouse gases cum climate change. While the burning of wood wastes results in CO₂ emission, decomposition generates methane. In place of these emissions, wood wastes can be converted into biochars which have a lot of novel applications. However, low biochar yield was the common limitation of wood wastes, essentially, due to a mixture of different classifications of trees that pyrolyse at different conditions. In this study, biochar yield from sorted wood wastes was optimised by varying pyrolysis temperature and time. Power consumption, cost, and carbon footprint of the optimised biochar and ash were compared for both hydropower grid and diesel generator scenarios. Optimal pyrolysis yields were 33.6 % (400 °C), 29.4 % (350 °C) and 18.5 % (400 °C) respectively for hardwood sawdust char (HSC), softwood sawdust char (SSC), and mixed sawdust char (MSC) at 2 hours duration for all materials. The CO₂ emissions from ash were 2.49 kg and 19.0 kg respectively for grid and diesel power supply. The diesel generator power was 17 times more expensive than grid power for wood wastes pyrolysis. Wood wastes have better biochar yield when charred homogenously; they have a smaller carbon footprint and are cheaper when produced with power from the grid. Wood wastes in place of being burnt can be processed as inexpensive and environment-friendly biochar.

This paper analyses and discusses the monthly and annual changes of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations from main sewage discharge ports in Xiangshan Bay. Using monitoring data obtained from 2010 to 2019, it systematically examines the monthly variation characteristics of the sewage discharge ports and the interannual changes in the fluxes of major pollutants into the sea. The concentrations of COD, TN, and TP, which were relatively high in November and January-March, generally declined. The annual and monthly changes fluctuated, but the flux into the sea generally decreased. The ecological environment of the nearby sea area is adversely affected, chiefly by land-based pollutants. During the five-year period, COD mainly came from soil erosion and domestic pollution, while TN and TP mainly came from agricultural activities and soil erosion. Hence, it is both necessary and urgent to improve the management of the sewage outfalls from land sources into the sea.

Abiotic and biotic bounty of riparian waters may be affected by inadequate maintenance works. Improper planning and execution of maintenance works cause changes to hydrological and hydrochemical condition of water in small rivers, affecting biocenose of riverbeds by modifying the taxonomic composition of organisms inhabiting the regulated river section. Five (5) rivers were subject to studies - Plonia, Mysla, Tywa, Rurzyca, and Wardynka (Odra river basin), which were monitored before and after maintenance works consisting in desilting, mowing and removal of aquatic plants. This study examined hydrological (mean depth and width of small rivers, speed and flow), physical and chemical parameter of water (temperature, pH, O₂, N-NO₃, N-NH₄, P-PO₄) before and after dredging of selected rivers. Obtained results and resulting statistical analysis demonstrated increase in hydrological indices - depth, width, speed and flow. Among other physical and chemical properties that significantly increased following completion of maintenance works, were O₂ and NH₄. NO₃ concentration and temperature dropped, but not statistically significant. Changes in hydrological and hydrochemical properties of waters caused by maintenance works may affect biodiversity of the regulated river sections, including changes in composition of ichthyofauna species.

The Danube River plays significant role not only for preserving natural ecosystems. The aim of this paper is to examine the Middle Danube water quality in the part flowing through Serbia in section Bezdan -Banatska Palanka. Water quality data were examined for seven control points for period 2004-2018, for seven parameters: suspended solids (SS), dissolved oxygen (DO), electrical conductivity (EC), nitrates (NO₃^–-N), total phosphorus (P_tot), biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD). Data analyses included the application of ANOVA, linear regression analysis and Mann-Kendall trend test. The Mann-Kendall tests in most (32/49) cases, i.e. in 65 %, confirmed the non-existence of a significant trend. Significant downward trends were confirmed in 17 cases. Water quality improvement was confirmed at following control points: Bezdan for NO₃^–-N, P_tot and BOD₅; Bogojevo for NO₃^–-N, P_tot, COD and BOD₅; Novi Sad for P_tot, BOD₅ and COD; Slankamen for BOD₅ and COD; Smederevo for NO₃^–-N and COD; Banatska Palanka for NO₃^–-N. Slight deterioration of water quality was confirmed only in two cases, at the Zemun and Smederevo where DO was decreasing. Water quality for the examined period was stable and can be characterised as excellent and/or very good (class I or class II). Results emphasise fact that water quality trends monitoring reveals river sectors where the process of water quality degradation is ongoing. Timely detected critical river sectors can draw the attention of decision-makers, who can improve the existing legislation that would lead to water quality improvement.

With the continuous operation of constructed wetlands, substrate clogging is issue. In order to solve the problem, there is practical significance to understand the causes for clogging in constructed wetlands. Two pilot-scale vertical flow constructed wetlands were established, namely, CW-B and CW-C. By studying the relationship between the accumulation of different substances and the banked-up water area, it was found that the accumulation of non-filter substances and total solids was an important reason for the clogging of the substrate, and the accumulation degree of non-filter inorganic substances was more obvious than that of non-filter organic substances, and the blockage was mainly located in the 10-20 cm layer. In the vertical flow constructed wetland with river sand as the main substrate, water accumulation will occur when the content of total solid and non-filter substances exceeds 67.233 g and 101.228 g per cubic meter of substrate, respectively. Therefore, it is important to pay attention to the substrate particle size matching of 0-20 cm layer to reduce the clogging in the vertical flow constructed wetland. The clogging has little effect on chemical oxygen demand (COD) removal, but great effect on total phosphorus (TP) removal. Compared with the control wetland (CW-C), the biomass content in the CW-B with biochar increased by 334.26 nmol P/g, which can improve the removal efficiency of total nitrogen (TN) and total phosphorus (TP), but also increase the risk of clogging in the vertical flow constructed wetland. Future research should try to combine the anti-blocking research results of biochar constructed wetlands to improve the purification effect, which is of great significance to promote the sustainable development of constructed wetlands.

The discharge of wastewater containing both high salinity and high organic content without prior treatment is detrimental to aquatic life and water hygiene. In order to integrate the advantages of membrane treatment and biological treatment, and exert the phosphorus removal efficiency of dewatered alum sludge, in this study, an aerobic membrane reactor based on dehydrated alum sludge was used to treat mustard tuber wastewater with salinity of 6.8-7.3 % under the conditions of 30 °C, 20 kPa trans-membrane pressure (TMP) and chemical oxygen demand (COD) of 3300-3900 mg/L. Three replicate reactors were applied to assess the operational performance under different organic loading rate (OLR). The results showed that all reactors were effective in removing COD, ammonia nitrogen (NH₄⁺-N) and soluble phosphate (SP) under the conditions of 30 °C and 20 kPa of TMP. Meanwhile, the effluent concentration of COD, NH₄⁺-N and SP all increased while OLR was changed from 1.0 to 3.0 kg COD/m³/day, and the effluent COD and NH₄⁺-N concentration except for SP could reach the B-level of Chinese “Wastewater quality standards for discharge to municipal sewers” when OLR was less than 3.0 kg COD/m³/day. This indicates that dewatered alum sludge-based aerobic membrane reactor is a promising bio-measure for treating high salinity wastewater.

For aerobic static composting, fresh cow, pig, and chicken manures were used as feedstock and mixed with 10 % corn straws, which was considered as the bulking agent. In the composting process of different livestock and poultry manures, the changing trends of temperature, pH, conductivity, density, and other parameters were intensively studied. The results were as follows: (1) after the tail biogases of composting systems - using cattle manure, pig manure, and chicken manure - were introduced into the biofilter, the concentration of O₂ decreased slightly, but the concentration of CO₂ increased. The odour in these tail biogases declined significantly, and thus the biodegradation of tail biogas was obvious. (2) The oxygen consumption in the different periods of the composting process of these three manures was almost the same, and the average oxygen consumption for the three manures was 0.928, 0.937, and 0.945 m³/kg, respectively. Under standard conditions, the density of oxygen is 1.429 g/L, and the average oxygen consumption in the composting processes of these three manures was 1.326, 1.338, and 1.350 kg/kg, respectively.

Macroinvertebrates of two ex-manor ponds located in Chroscina, Opole Region (Poland) were studied from 2015 to 2018 to investigate their community composition and diversity and evaluate the heterogeneity of communities on spatial and temporal scale referring to environmental variables and revitalisation work. A total of 32 taxa were recorded (at the family level, except Oligochaeta), 13 of which were Ephemeroptera, Odonata and Trichoptera, recognised as sensitive groups in lentic ecosystems. Macroinvertebrate richness and diversity varied considerably, especially in spring and summer. It was found that habitat heterogeneity influenced benthic invertebrates more than basic water parameters. However, the environmental variables together accounted for only 38 % of the observed variations. Thus, other factors, such as fish predation, may have played a leading role in community shaping. The distinct differences between pond communities, four years after the revitalisation works, resulted more from different habitat features than from the previous sediment removal.

Nitrate reductase (NR) and nitrite reductase (NiR) play important roles in nitrate assimilation in plants. Previous studies have indicated that NR and NiR in eelgrass may contribute to its NaCl tolerance. This study investigated the expression characteristics and the biological functions of NR and NiR in eelgrass (Zostera marina), named as ZmNR and ZmNiR, were cloned, characterised and overexpressed in both bacteria and tobacco. The open reading frames of ZmNR and ZmNiR contain 2628 and 1773 nucleotides that encode 875 and 590 amino acids respectively. Amino acid sequence alignment indicated that the purported ZmNR and ZmNiR proteins presented low homology with other plant NR and NiR sequences. Real-time quantitative PCR revealed that the expression of ZmNR and ZmNiR was supressed when exposed to low salinity and induced by high salinity. Further physiological analyses demonstrated that blocking nitrate assimilation by adding Na₂WO₄ in eelgrass reduced its tolerance to NaCl stress. The heterologous expression of the ZmNR and ZmNiR genes in Escherichia coli and Nicotiana benthamiana could confer tolerance to NaCl stress. Physiological and growth analyses suggested that ZmNR and ZmNiR in plants could resist NaCl stress by regulating various physiological pathways and biochemical processes triggered by nitric oxide (NO). Taken together, these results suggested that NR-dependent NO synthesis may play an important role in NaCl tolerance in eelgrass.