Naim Rashid

The extremophilic microalga Galdieria sulphuraria has shown considerable potential for the treatment of acid mine drainage (AMD) while producing biomass for value-added applications. However, biological metal removal alone is limited, and efficient biomass harvesting under highly acidic conditions remains a major challenge. This study developed an integrated treatment approach with potential sustainability benefits by cultivating Galdieria sulphuraria in AMD followed by simultaneous biomass harvesting and dissolved metal removal using calcium polysulfide (CaSx). Galdieria sulphuraria successfully grew in undiluted Berkeley Pit water (BPW), a representative AMD, demonstrating its adaptability to highly acidic and metal-rich conditions. During cultivation, only partial removal of dissolved metals was achieved, indicating that biological treatment alone was insufficient for effective AMD remediation. Conventional flocculants, ferric chloride and chitosan, achieved only moderate harvesting efficiencies (54–56%) and showed negligible contribution to metal removal. In contrast, CaSx achieved a maximum biomass harvesting efficiency of 98.7% after a 60min settling-time experiment. In a separate dosage experiment, Zn removal reached nearly 100% at 2.95 g L⁻¹ of CaSx, while Mn removal increased with CaSx dosage and reached 78% at 7.36 g L⁻¹. Control experiments with BPW in the absence of microalgae showed comparable metal removal, indicating that Zn and Mn removal using CaSx treatment was primarily driven by chemical processes. The enhanced treatment was consistent with sulfide-mediated precipitation of dissolved metals and the increase in solution pH, which promoted the formation of dense biomass aggregates. CHN, SEM, EDX, and XRD analyses consistently demonstrated that CaSx transformed the recovered material from predominantly organic microalgal biomass into a mineral-enriched biomass composite. This study demonstrates that integrating Galdieria sulphuraria cultivation with CaSx-assisted biomass harvesting and dissolved metal removal provides a potential approach for sustainable AMD remediation while generating a mineral-enriched biomass.

This study aims to treat juice industry wastewater and recover resources using purple non-sulfur bacteria (PNSB). Simulated juice wastewater was prepared and used as a feedstock for PNSB. Carbon sources, including sucrose, fructose, glucose, and tris-Na-citrate, were added to different bottles separately and inoculated with a mixed culture of PNSB. Tris-Na-citrate showed higher growth and biomass production (650±70 mg/L) than the other carbon sources. The PNSB growth was associated with the pH change; tris-Na-citrate showed different pH change behavior than the other carbon sources, i.e., it showed a lesser decrease in the medium pH than the others. The effect of substrate (using glucose) concentration on PNSB biomass production was determined in the following experiment. A substrate concentration of 400 mg/L (as COD) showed the highest growth, whereas 800 mg/L (as COD) returned the highest biomass production (776±1 mg/L). Total organic carbon removal (TOC) increased with an increase in substrate concentration. Inorganic carbon removal initially decreased but then increased over the growth period; however, it was also directly correlated with initial substrate concentration. Lastly, the effect of pH on TOC, IC, and COD removal was investigated. A pH of 6.0 or above (up to 8.0) was required to remove organic and inorganic carbon.

Fruit juice industry wastewater is characterized by high chemical oxygen demand (COD) and low pH, which requires extensive energy if treated aerobically and can adversely affect aquatic organisms if discharged into water bodies without proper treatment. In this study, purple non-sulfur bacteria (PNSB) were employed to recover carbon through photoanaerobic treatment in the form of single-cell protein (SCP) suitable for aquaculture and rich in carotenoid and bacteriochlorophyll photopigments. The efficacy of PNSB was investigated using two types of wastewaters, citrus juice wastewater (CJW), and mixed juice wastewater (MJW) as substrates at different pH conditions (5.0–8.0). pH 8.0 showed the highest COD removal in CJW (89 ± 0.1%) and pH 7.0 in MJW (94 ± 1%), respectively. The biomass yields were 0.493 g-VSS·g-COD⁻¹ and 0.397 g-VSS·g-COD⁻¹ for CJW and MJW. SCP contents in CJW and MJW were 48 ± 1% and 40 ± 3%, respectively. Pigment analysis revealed that PNSB biomass contained carotenoids and bacteriochlorophyll. Carotenoids in CJW and MJW were 1354 ± 64 µg·g⁻¹ and 1558 ± 218 µg·g⁻¹ of biomass; bacteriochlorophyll contents were 2097 ± 110 µg·g⁻¹ and 3100 ± 614 µg·g⁻¹ of biomass, respectively. The microbial population showed diversity among the two substrates and pH conditions, with PNSB comprising potentially up to 51% of microbes in the culture. The results demonstrate that PNSB could be used as potential mediators to treat fruit juice wastewater, and produce SCP, and photopigments simultaneously.

Background: Bioenergy attracts much attention due to the global demand for renewable and sustainable energy resources. Waste biomass feedstocks—date pits, coffee waste, and cow dung—require efficient and environmentally friendly waste-management technologies such as pyrolysis. Fast pyrolysis occurs at fast heating rates (10–100 °C/s), generates high bio-oil yields, and is the most widely used process for biofuel generation. The aim of the study is to compare the effect of pyrolysis between single, binary, and ternary feeds on thermal degradation behavior and bio-oil composition. Methods: Thermogravimetric analysis (TGA) was conducted at 30 °C/min from room temperature to 850 °C to understand the thermal degradation behavior of the biomasses. A Pyroprobe^® reactor—a micro-scale pyrolyzer—was used to conduct the fast pyrolysis at 500 °C with a heating rate of 10 °C/s, and the volatile contents were quantified using a gas chromatograph–mass spectrometer (GC/MS). Results: The (TGA) showed three main stages of decomposition following dehydration, devolatilization, and char degradation for the different single and multiple feeds. According to the identified compounds, the bio-oil components are broadly identified as aldehydes, amines, aliphatic, aromatics, alcohols, furans, ketones, and acids. The three single-biomass pyrolysis products have four compounds in common, acetic acid and ketone groups (acetic acid, 2-propanone, 1-hydroxy-, benzyl methyl ketone, and 1,2-cyclopentanedione). Conclusion: The bio-oil generated from the feeds comprises great potential for volatiles, diesel, and gasoline production with carbon atoms ranging from C2–C33. Future studies should focus on understanding the effect of procedural parameters, including blending ratio, temperature, and heating rates, on bio-oil composition. Additional molecular techniques should be employed to understand biomass components’ reaction mechanisms to produce useful bio-oil products.

In recent years, single-cell protein (SCP) has been considered a promising aquaculture feed to cope with the growing issue of food security. SCP is derived from microbes including algae, yeasts, and bacteria. Algae and yeasts have been comprehensively studied as SCP sources in the last few years. However, their large-scale application is not yet economical. Recently, the use of purple non-sulfur bacteria (PNSB) has been realized as a sustainable source of SCP. PNSB display unique metabolic features that distinguish them from other SCP sources. They can grow under various light and electron donor/acceptor conditions, can use a variety of low-cost carbon sources, give high substrate yield under their preferred photoheterotrophic growth mode, and demonstrate anti-pathogenic properties. They also use the infrared region of light that enables their straightforward enrichment under non-axenic conditions. Despite the unique characteristics of PNSB, their use as SCP has not been widely reported. This review provides comprehensive knowledge about different factors that influence the quality and quantity of SCP produced from PNSB. The effects of key factors including light, redox conditions, trace metals, carbon substrate, and substrate availability are discussed. Special focus is given to the use of PNSB as SCP in aquaculture and PNSBs concomitant role in improving water quality. This information would expand knowledge and enhance understanding to utilize PNSB as an alternative SCP source for aquaculture feed.

This study investigated the growth-dependent role of algal organic matters (AOMs) to achieve high removal efficiency (R.E) of microalgae. The results showed that the microalgae cells produced 96 ± 2% of total AOMs as loose bound AOMSS (LB-AOMs) and 4 ± 1% as cell-bound (CB-AOMs) in exponential phase. In stationary phase, LB-AOMs and CB-AOMs were 46 ± 0.7percentage and 54 ± 0.2 percentage, respectively. The R.Es in exponential and stationary phase were 83 ± 2.6% and 66 ± 1.2%, respectively. It is found that the difference of biomass concentration (between exponential and stationary phase) had no significant impact on the R.E (P > 0.01). Further investigations revealed that LB-AOMs inhibit flocculation in exponential and CB-AOMs in stationary phase; however, CB-AOMs showed stronger inhibition than the LB-AOMs (P < 0.01). The provision of calcium (17 ± 0.9 mg/L) to the culture reduced the AOMs inhibition and improved the R.E from 66 ± 1.2% (in control) to 90 ± 4.2%. An increase in R.E was attributed to the interaction of calcium with AOMs and subsequently acting as a flocculant. The findings of this study can be valuable to improve the performance of auto-flocculation technology, which is mainly limited by the presence of AOMs. Graphical Abstract