Treatment of clean in place (CIP) wastewater using microalgae: Nutrient upcycling and value-added byproducts production

Tertiary treatment of dairy wastewater applying a microalga-fungus consortium

This paper aimed to apply filamentous fungi (Penicillium oxalicum and Cunninghamella echinulata), the microalga Tetradesmus obliquus and their co-culture in advanced treatment (tertiary treatment) of cheese whey. The bioremediation process was carried out in agitated flasks and bubble column bioreactors with different concentrations of chemical oxygen demand (COD) (223-1663 mg L-1), total nitrogen (TN) (13-61 mg L-1), and total phosphorus (TP) (3-26 mg L-1). The results obtained in shaken flasks showed a superiority of the consortium compared to the systems with separated species. In this sense, the treatment was carried out in a bubble column reactor, and the consortium formed by the microalga and the fungus C. echinulata showed a greater efficiency (at a light intensity of 100 µmol m-2 s-1), promoting by the symbiosis to reach removal efficiencies of up to 93.7, 78.8 and 93.4% for COD, TN and TP, respectively; meeting Brazilian and European standards for discharge into water bodies. In addition, no pH adjustment was required during the co-culture treatment, demonstrating the buffering effect of using these two types of microorganisms. Therefore, the use of the consortium formed by T. obliquus and C. echinulata as a remediator was highly promising to promote the advanced treatment of cheese whey.

Current trends and possibilities of typical microbial protein production approaches: a review

Global population growth and demographic restructuring are driving the food and agriculture sectors to provide greater quantities and varieties of food, of which protein resources are particularly important. Traditional animal-source proteins are becoming increasingly difficult to meet the demand of the current consumer market, and the search for alternative protein sources is urgent. Microbial proteins are biomass obtained from nonpathogenic single-celled organisms, such as bacteria, fungi, and microalgae. They contain large amounts of proteins and essential amino acids as well as a variety of other nutritive substances, which are considered to be promising sustainable alternatives to traditional proteins. In this review, typical approaches to microbial protein synthesis processes were highlighted and the characteristics and applications of different types of microbial proteins were described. Bacteria, fungi, and microalgae can be individually or co-cultured to obtain protein-rich biomass using starch-based raw materials, organic wastes, and one-carbon compounds as fermentation substrates. Microbial proteins have been gradually used in practical applications as foods, nutritional supplements, flavor modifiers, and animal feeds. However, further development and application of microbial proteins require more advanced biotechnological support, screening of good strains, and safety considerations. This review contributes to accelerating the practical application of microbial proteins as a promising alternative protein resource and provides a sustainable solution to the food crisis facing the world.

Biodegradability and bioavailability of dissolved substances in aquaculture effluent: Performance of indigenous bacteria, cyanobacteria, and green microalgae

Aquaculture is a controlled aquatic farming sector and one of the most important human food sources. Fish farming is one of the predominant, fast-growing sectors that supply seafood products worldwide. Along with its benefits, aquaculture practices can discharge large quantities of nutrients into the environment through non-treated or poorly treated wastewater. This study aims to understand the nutrient composition of fish wastewater and the use of indigenous bacteria, cyanobacteria, and microalgae as an alternative biological treatment method. Wastewater samples from a local fish farming facility were collected and treated using six different species of cyanobacteria and microalgae include Chroococcus minutus, Porphyridium cruentum, Chlorella vulgaris, Microcystis aeruginosa, Chlamydomonas reinhardtii, and Fischerella muscicola. All the samples were incubated for 21 days, and the following parameters were measured weekly: Chemical oxygen demand (COD), phosphate, total dissolved nitrogen, and dissolved inorganic nitrogen. In addition, dissolved organic nitrogen (DON), bioavailable DON (ABDON), and biodegradable DON (BDON) were calculated from the mass-balance equations. Colorimetric and digestive methods were used for the parameter measurements. The results showed that C. reinhardtii reduced the soluble COD concentration by 74.6 %, DON by 94.3 %, and phosphorous by more than 99 %. Moreover, M. aeruginosa, and C. minutus significantly reduced inorganic nitrogen species (>99 %). This alternative fish wastewater treatment method was explored to gain insight into fish wastewater nutrient composition and to create a sustainable alternative to conventional fish wastewater treatment methods.

Clean-In-Place (CIP) wastewater management using nanofiltration (NF)-forward osmosis (FO)-direct contact membrane distillation (DCMD): Effects of draw salt

A substantial amount of water is being used during Clean-in-Place (CIP) operation, and is transformed into wastewater that can cause eutrophication to the nearby ecosystem. The present study proposed the Nanofiltration (NF) - Forward Osmosis (FO) - Direct Contact Membrane Distillation (DCMD) to recover the cleaning agents and reclaim freshwater from the model CIP wastewater. NF steps were suggested as prefiltration steps to remove organic compounds from the CIP wastewater. NF steps reduced the lactose and protein contents by 100 % and 95.6 %, respectively. The permeates from NF steps were further managed by the integrated FO-DCMD system. Several draw salts such as NaCl, KCl, MgCl2, and CaCl2 were compared to investigate the influence on FO and DCMD performance. It was found that monovalent salts (NaCl and KCl) outperformed the divalent salts (MgCl2 and CaCl2) in terms of water flux for both FO and DCMD. This can be attributed to the lower viscosity and higher mass transfer coefficient. In addition, the replenishment costs of each salt were evaluated since salts loss occurred during FO and DCMD operation. The cost evaluation revealed that NaCl is most the cheapest salts per reclaimed water. All of this observation indicates that NaCl is preferred in terms of water flux and replenishment cost. The NF permeate kept concentrated using the integrated FO-DCMD or single FO with 2 M of NaCl. Compared to a single FO that showed a consistent decline in draw solution concentration, FO-DCMD could maintain the concentration of the draw solution. Despite the constant concentration, flux decline of FO was observed due to fouling formation caused by the high-temperature operation. However, the FO-DCMD could accomplish the recovery of pure water. Finally, the cleaning agents recovered by the NF-FO-DCMD showed the cleaning efficacy comparable to the fresh NaOH. These results suggest the potential of the proposed system to manage the CIP wastewater.

A step forward in sustainable pesticide production from Amphidinium carterae biomass via photobioreactor cultivation with urea as a nitrogen source

This study addresses the problem of replacing nitrate and ammonium with urea as a greener nitrogen source in the mass cultivation of the microalga Amphidinium carterae for the development of amphidinol-based phytosanitary products. To solve this problem, a nuclear magnetic resonance assisted investigation evaluated the effect of nitrogen sources on growth and metabolic profiles in photobioreactors. Urea-fed cultures exhibited growth kinetics comparable to nitrate-fed cultures (µmax = 0.30 day-1, Pbmax = 43 mgL-1day-1). Urea-fed cultures had protein, lipid, and carbohydrate contents of 39.5%, 14.5%, and 42.4%, respectively, while nitrate-fed cultures had 27.9 %, 17.5% and 48.1%, respectively. Metabolomics revealed nitrogen source-dependent metabotypes and a correlation between amphidinols and polyunsaturated fatty acids. The amphidinol-to-nitrogen yield coefficient in urea-fed cultures (135 mg/g) was approximately 2.5 times higher than in nitrate-fed cultures. The potent antiphytopathogenic activity exhibited by extracts from urea-fed cultures underscores the potential of urea as a sustainable nitrogen source in microalgae-based biorefineries.

Microalgae-Based Biotechnology as Alternative Biofertilizers for Soil Enhancement and Carbon Footprint Reduction: Advantages and Implications

Due to the constant growth of the human population and anthropological activity, it has become necessary to use sustainable and affordable technologies that satisfy the current and future demand for agricultural products. Since the nutrients available to plants in the soil are limited and the need to increase the yields of the crops is desirable, the use of chemical (inorganic or NPK) fertilizers has been widespread over the last decades, causing a nutrient shortage due to their misuse and exploitation, and because of the uncontrolled use of these products, there has been a latent environmental and health problem globally. For this reason, green biotechnology based on the use of microalgae biomass is proposed as a sustainable alternative for development and use as soil improvers for crop cultivation and phytoremediation. This review explores the long-term risks of using chemical fertilizers for both human health (cancer and hypoxia) and the environment (eutrophication and erosion), as well as the potential of microalgae biomass to substitute current fertilizer using different treatments on the biomass and their application methods for the implementation on the soil; additionally, the biomass can be a source of carbon mitigation and wastewater treatment in agro-industrial processes.

Effects of light source and inter-species mixed culture on the growth of microalgae and bacteria for nutrient recycling and microalgae harvesting using black odorous water as the medium

To achieve the sustainable and effective removal efficiency of nutrients in black odorous water, light source, inter-species microalgae mixed culture, and the harvesting effect were all explored. The results showed that under a LED light source, the addition of interspecific soluble algal products (SAP) promoted the growth of Haematococcus pluvialis (H. pluvialis) M1, and its maximum specific growth rate was 1.76 times that of H. pluvialis cultivated alone. That was due to the hormesis effect between the two kinds of microalgae, the SAP produced by Scenedesmus could stimulate the growth of H. pluvialis. The algae and bacteria symbiotic system with black odorous water as the medium showed excellent performance to treat nutrients, where the concentration of ammonia nitrogen (NH₃-N) and total phosphorus (TP) (0.84, 0.23 mg/L) met the requirements of landscape water. The microbial diversity analysis revealed that the introduction of microalgae changed the dominant species of the bacterial community from Bacteroidota to Proteobacteria. Furthermore, timely microalgae harvesting could prevent water quality from deteriorating and was conducive to microalgae growth and resource recycling. The higher harvest efficiency (98.1%) of H. pluvialis was obtained when an inoculation size of 20% and 0.16 g/L FeCl₃ were provided.

Evaluation of the effects of input variables on the growth of two microalgae classes during wastewater treatment

Wastewater treatment carried out by microalgae is usually affected by the type of algal strain and the combination of cultivation parameters provided during the process. Every microalga strain has a different tolerance level towards cultivation parameters, including temperature, pH, light intensity, CO2 content, initial inoculum level, pretreatment method, reactor type and nutrient concentration in wastewater. Therefore, it is vital to supply the right combination of cultivation parameters to increase the wastewater treatment efficiency and biomass productivity of different microalgae classes. In the current investigation, the decision tree was used to analyse the dataset of class Trebouxiophyceae and Chlorophyceae. Various combinations of cultivation parameters were determined to enhance their performance in wastewater treatment. Nine combinations of cultivation parameters leading to high biomass production and eleven combinations each for high nitrogen removal efficiency and high phosphorus removal efficiency for class Trebouxiophyceae were detected by decision tree models. Similarly, eleven combinations for high biomass production, nine for high nitrogen removal efficiency, and eight for high phosphorus removal efficiency were detected for class Chlorophyceae. The results obtained through decision tree analysis can provide the optimum conditions of cultivation parameters, saving time in designing new experiments for treating wastewater at a large scale.