Application of Fruit Wastes as Cost-Effective Carbon Sources for Biological Sulphate Reduction

Proper C/N ratio enhances the effect of plant diversity on nitrogen removal and greenhouse effect mitigation in floating constructed wetlands

Treating wastewater with low carbon-to-nitrogen (C/N) ratios by constructed wetlands (CWs) is still problematic. Adding chemicals is costly and may cause secondary pollution. Configuring plant diversity in substrate-based CWs has been found to be a better way to treat low-C/N wastewater, but wastewater treatment in floating CWs needs to be studied. In this study, wastewater with C/N ratios of 5 and 10 were set in simulated floating CWs, and 9 combinations with plant species richness (SR) of 1, 3, and 4 were configured. The results showed that (1) increasing SR improved the total N mass removal (NMR) by 29% at a C/N ratio of 5 but not 10; (2) the presence of Oenanthe javanica in the microcosms increased the NMR by 13% and 20% with C/N ratios of 5 and 10, respectively; (3) increasing SR mitigated the net global warming potential (GWP) by 120% at a C/N ratio of 5 but not 10; and (4) a Hemerocallis fulva × O. javanica × Echinodorus parviflours × Iris hybrids mixture resulted in a high NMR and low net GWP. In summary, assembling plant diversity in floating CWs is an efficient and clean measure during the treatment of wastewater with a C/N ratio of 5.

Recent Advances in Biotechnologies for the Treatment of Environmental Pollutants Based on Reactive Sulfur Species

The definition of reactive sulfur species (RSS) is inspired by the reactivity and variable chemical valence of sulfur. Sulfur is an essential element for life and is a part of global geochemical cycles. Wastewater treatment bioreactors can be divided into two major categories: sulfur reduction and sulfur oxidation. We review the origins of the definition of RSS and related biotechnological processes in environmental management. Sulfate reduction, sulfide oxidation, and sulfur-based redox reactions are key to driving the coupled global carbon, nitrogen, and sulfur co-cycles. This shows the coupling of the sulfur cycle with the carbon and nitrogen cycles and provides insights into the global material-chemical cycle. We also review the biological classification and RSS metabolic mechanisms of functional microorganisms involved in the biological processes, such as sulfate-reducing and sulfur-oxidizing bacteria. Developments in molecular biology and genomic technologies have allowed us to obtain detailed information on these bacteria. The importance of RSS in environmental technologies requires further consideration.

Assembling plant diversity mitigates greenhouse gas emissions and achieves high nitrogen removal when treating the low-C/N wastewater by constructed wetlands

The low carbon-to-nitrogen (C/N) ratio in wastewater will inhibit pollutant removal, and more seriously, it will cause an increment of nitrous oxide (N₂O) emissions of constructed wetlands (CWs). Raising the C/N ratio of wastewater is an effective way to solve this problem, while it may cause secondary pollution and is costly. Assembling plant diversity promotes N removal, while the effects of plant diversity and increasing C/N ratio on global warming potential (GWP) combined by N₂O and methane (CH₄) are lack of comparison. In this study, 108 CW microcosms were established to explore the effects of increasing the C/N ratio from 1 to 5 and assembling plant diversity on N removal and GHG emissions. Results showed that when the C/N ratio was 1, (1) increasing species richness reduced N₂O and CH₄ emissions then reduced the GWP by 70%; (2) the presence of Arundo donax in microcosms reduced GWP by 72%; (3) an A. donax × Tradescantia fluminensis × Reineckia carnea mixture resulted in a high N removal and decreased the GWP per g N removal by 92% with a cost increment of 0.05 USD per m³ wastewater treated; and (4) as the C/N ratio increasing to 5, the GWP per g N removal of monocultures was reduced by 96%, but the cost increased by at least 0.29 USD per m³ wastewater treated. In summary, configuring plant diversity in CWs is an efficient, clean, and cost-effective measure to treat wastewater with a low C/N ratio.

Coupling wastewater valorization with sustainable biofuel production: Comparison of lab- and pilot-scale biomass yields of Chlorella sorokiniana grown in wastewater under photoautotrophic and mixotrophic conditions

Microalgae are the important biofuel precursors and their economic cultivation can be boosted under mixotrophic (MT) conditions while employing different industrial wastewaters containing organic carbon. In the current research, the quantitative analysis of microalgal biomass production under MT and photoautotrophic (PT) cultivation conditions both at lab and pilot scales was studied. For the purpose, a pre-identified microalgal species Chlorella sorokiniana was cultivated mixotrophically and photoautotrophically at lab and pilot scales. Artificially prepared wastewater containing 2% (w/v) sugarcane molasses was used for MT cultivation. However, for PT cultivation, atmospheric CO₂ was the only carbon source. After 15 days of aerobic incubation, microalgal biomass was harvested and analyzed for biomass productivity. Cultivation conditions and cultivation scale posed significant and non-significant impact, respectively on biomass productivities. However, biomass productivity was comparatively higher for the biomass raised under MT conditions at lab scale. The recorded values of biomass productivity were 88.75 ± 9.51 and 127.68 ± 7.91 mg L^-1 d^-1 for the biomass raised at lab scale under PT and MT conditions, respectively. Pilot-scale cultivation depicted biomass productivities as 83.49 ± 7.87 and 124.88 ± 3.76 mg L^-1 d^-1 under PT and MT conditions, respectively. High biomass production under MT conditions may suggest the elevated production of biofuels from microalgae. Future studies on biomass production while utilizing different industrial wastewaters at pilot scale and in open raceway ponds are needed for viable production of microalgae-based fuels.

Towards sustainable wastewater treatment: Influence of iron, zinc and aluminum as anode in combination with salt bridge on microbial fuel cell performance

Microbial fuel cell (MFC) is a green technology and does not harm the environment. It can be used for wastewater treatment, hydrogen production and power generation. There are lot of avenues need to be investigated to increase the efficiency of MFC and in order to make it acceptable publicly. Efficiency of MFC depends on many factors. In this study, the influence of anode materials (Fe, Al and Zn), their sizes (12, 16 and 20 cm²) and shapes (square, rectangular and circular) were investigated on MFC efficiency. Dual chamber MFC setup was prepared in which Rhodobacter capsulatus was used as biocatalytic agent. Results revealed that Zn anode gave the highest voltage of 1.57 V with corresponding 0.23 A of current. Size of 20 cm² of anode gave maximum voltage of 1.66 V with corresponding value of 0.08 A current, while anode size of 16 cm² gave maximum current of 0.75 A with corresponding voltage of 1.65 V. Regarding their studied shapes, circular shape of anode gave the highest voltages of 1.70 V. Salt bridge played an important role in internal resistance of the fuel cell. The results were checked by changing the diameter and length of the salt bridge. The best results were noticed with 16 cm² circular Zn anode and Fe as cathode. Salt bridge with 7.5 cm length gave the highest voltage of 1.65 V, while 4 gauge diameter salt bridge gave the highest current of 0.85 A.

Uptake of Cu2+ by unicellular microalga Chlorella vulgaris from synthetic wastewaters is attenuated by polystyrene microspheres

Aquatic and terrestrial ecosystems are receiving micro- and macro-plastic pollutants alarmingly from various anthropogenic activities. The complications caused by microplastics are largely unexplored and need substantial studies. In the current study, we investigated the repressive effects of negatively and positively charged polystyrene microspheres of two variable sizes (0.05 and 0.5 μm) on functioning of unicellular green microalgae. For the purpose, a pollution-resistant microalgal species was isolated and identified by 18 S rRNA gene sequencing as Chlorella vulgaris. The functioning of the pure-cultured microalgal cells was then assessed in terms of their better metal (Cu²⁺) uptake potential with and without the provision of PS microspheres. The algal cells up took Cu²⁺ significantly (90% at 75 mg/L) after 15 days of aerobic incubation. However, positively charged polystyrene microspheres remarkably affected the uptake of Cu²⁺ and it was comparatively reduced to almost 50%, while negatively charged microspheres couldn't influence the Cu²⁺ uptake potential of C. vulgaris. In addition, size of the microspheres insignificantly affected the metal uptake potential of the microalgae. Unveiled facts of this investigation will be helpful for designing economical and efficient remedial systems based on the in-situ implication of microalgae.