Soil extracts are useful nutrients to enhance the growth of microalgae. Therefore, the present study attempts for the use of virgin soils from Peninsular Malaysia as growth enhancer. Soils collected from Raja Musa Forest Reserve (RMFR) and Ayer Hitam Forest Reserve (AHFR) were treated using different extraction methods. The total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and dissolved organic carbon (DOC) concentrations in the autoclave methods were relatively higher than natural extraction with up to 132.0 mg N/L, 10.7 mg P/L, and 2629 mg C/L, respectively for RMFR. The results of TDN, TDP, and DOC suggested that the best extraction methods are autoclaved at 121 °C twice with increasing 87%, 84%, and 95%, respectively. Chlorella vulgaris TRG 4C dominated the growth at 121 °C twice extraction method in the RMRF and AHRF samples, with increasing 54.3% and 14%, respectively. The specific growth rate (µ) of both microalgae were relatively higher, 0.23 d⁻¹ in the Ayer Hitam Soil. This extract served well as a microalgal growth promoter, reducing the cost and the needs for synthetic medium. Mass production of microalgae as aquatic feed will be attempted eventually. The high recovery rate of nutrients has a huge potential to serve as a growth promoter for microalgae.

The assessment of water-extractable organic matter using an autoclave can provide useful information on physical, chemical, and biological changes within the soil. The present study used virgin forest soils from Chini Forest Reserve, Langkawi Island, and Kenyir Forest Reserve (Malaysia), extracted using different extraction methods. The dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and ammonium-nitrate content were higher in the autoclave treatments, up to 3.0, 1.3, 1.2, and 1.4 times more than by natural extraction (extracted for 24 h at room temperature). Overall, the highest extractable DOC, TDN, TDP, ammonium and nitrate could be seen under autoclaved conditions 121 °C 2×, up to 146.74 mg C/L, 8.97 mg N/L, 0.23 mg P/L, 5.43 mg N mg/L and 3.47 N mg/L, respectively. The soil extracts became slightly acidic with a higher temperature and longer duration. Similar trends were observed in the humic and nonhumic substances, where different types of soil extract treatments influenced the concentrations of the fractions. Different soil extraction methods can provide further details, thus widening the application of soil extracts, especially in microbes.

Microalgae are widely utilized in commercial industries. The addition of a modified artificial medium (soil extract) could enhance their growth. Soil extract collected from the Raja Musa peat swamp and mineral soil from the Ayer Hitam Forest Reserve (AHFR), Selangor, Malaysia, were treated using various extraction methods. Carteria radiosa PHG2-A01, Neochloris conjuncta, and Nephrochlamys subsolitaria were grown in microplates at 25 °C, light intensity 33.75 µmol photons m⁻²s⁻¹ for 9 days. N. conjuncta dominated the growth in 121 °C twice extraction method AFHR samples, with 47.17% increment. The highest concentrations of ammonia and nitrate were detected in the medium with soil extract treated with 121 °C twice extraction method, yielding the concentrations of 2 mg NL⁻¹ and 35 mg NL⁻¹ for ammonia and nitrate of RM soil and 2 mg NL⁻¹ and 2.85 mg NL⁻¹ for the AH soil. These extracts are proved successful as a microalgal growth stimulant, increasing revenue and the need for enriched medium. The high rate of nutrient recovery has the potential to serve as a growth promoter for microalgae.

The microalgae-based industries are trending upwards, particularly as the feed ingredient for aquaculture. Therefore, a sustainable and reasonably priced source of nutrients to support the mass cultivation of microalgae is in great demand. The present study explored the feasibility of using extracts from virgin soil as natural growth-promoting nutrients for the cultivation of Nannochloropsis oculata, Nannochloropsis oceanica, and Chlorella sorokiniana. The extracts were obtained from Bera Lake Forest using five different treatment methods. The greatest retrieval of dissolved organic carbon, total dissolved nitrogen, and total dissolved phosphorus were observed with the autoclave treatment method at 121 °C twice, yielding a respective concentration of 336.56 mg/L, 13.40 mg/L, and 0.14 mg/L, respectively. The highest growth was recorded with Nannochloropsis oculata resulting in an optical density of 0.488 ± 0.009 (×10³ cell mL⁻¹), exhibiting 43% and 44% enhanced growth in comparison to Nannochloropsis oceanica and Chlorella sorokiniana, respectively. The specific growth rate (0.114 ^a ± 0.007 d⁻¹) was the highest for Nannochloropsis oculata when the 24 h-extraction method was used, whereas the utilization of the autoclave 121 °C twice treatment method contributed to the highest specific growth of Nannochloropsis ocenica (0.069 ^a ± 0.003 d⁻¹) and Chlorella sorokiniana (0.080 ^a ± 0.001 d⁻¹). Collectively, these findings suggested that the addition of soil extracts which is sustainable and inexpensive promoted the growth of microalgae compared to the control system. A further study investigating the optimum culture conditions for enhanced microalgae growth will be carried out for the mass production of microalgae biomass.

Treatment of pollutants in water through bioremediation techniques has created great interest as it is environmentally friendly, low cost and highly efficient. The removal efficiency of methylene blue from aqueous by using low temperature (300 °C) banana pseudo stem biochar as adsorbent was studied. Batch adsorption experiments were carried out to determine the effect of pH (3 – 9), adsorbent dosage (0.05 g – 0.30 g) and contact time (10 min – 120 min). By using the methylene blue concentration of the initial and final adsorbed solution measured with UV-VIS Spectrophotometer, the removal efficiency of methylene blue and adsorption capacity of banana pseudo stem biochar were calculated. The results showed that maximum adsorption occurred at 99% of methylene blue removal efficiency with solution of pH 7, the adsorbent dosage was 0.25 g and contact time was 90 min. The adsorption isotherms were well described by both Langmuir and Freundlich models. Nevertheless, the experimental results were better fit with the Freundlich model. The adsorption kinetic analysis showed that the data complied well with the pseudo-second order model, indicating the chemisorption mechanism. It was concluded that banana pseudo stem biochar showed a good potential as an effective adsorbent for methylene blue dye removal from aqueous solution.