Simultaneous production of algal biomass and lipid by heterotrophic cultivation of linoleic acid-rich oleaginous microalga Chlorella sorokiniana using high acetate dosage.

The low-cost carbon source, acetate, was utilized to feed a linoleic acid-rich Chlorella sorokiniana for microalgal biomass and lipid accumulation. Remarkably high tolerance capability to high acetate dosage up to 30 g/L was observed, with heterotrophy being the preferred trophic mode for algal growth and lipogenesis when supplemented 20 g/L acetate. Transcriptome analysis revealed a marked activation of pathways involved in acetate bioconversion and lipogenesis upon exposure to high-level of acetate. However, the enhancement of photorespiration inhibited photosynthesis, which ultimately led to a decrease in biomass and lipid under mixotrophy. Heterotrophic acetate-feeding generated more superior amino acid profiling of algal biomass and a predominant linoleic acid content (50 %). Heterotrophic repeat fed-batch strategy in 5 L fermenter significantly increased the growth performance and lipid titer, with the highest levels achieved being 23.4 g/L and 7.0 g/L, respectively. This work provides a viable approach for bio-products production through acetate-based heterotrophic algal cultivation.

Genomics and metabolic characteristics of simultaneous heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal by Acinetobacter indicus CZH-5.

This study provides for the first time a systematic understanding of Acinetobacter indicus CZH-5 performance, metabolic pathway and genomic characteristics for aerobic nitrogen (N) and phosphorus (P) removal. Acinetobacter indicus CZH-5 showed promising performance in heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal. Under optimal conditions, the maximum ammonia-N, total nitrogen and orthophosphate-P removal efficiencies were 90.17%, 86.33%, and 99.89%, respectively. The wide tolerance range suggests the strong environmental adaptability of the bacteria. The complete genome of this strain was reconstructed. Whole genome annotation was used to re-construct the N and P metabolic pathways, and related intracellular substance metabolic pathways were proposed. The transcription levels of related functional genes and enzyme activities further confirmed these metabolic mechanisms. N removal was achieved via the nitrification-denitrification pathway. Furthermore, CZH-5 exhibited significant aerobic P uptake, with phosphate diesters as the main species of intracellular P.

Simultaneous aerobic nitrogen and phosphate removal capability of novel salt-tolerant strain, Pseudomonas mendocina A4: Characterization, mechanism and application potential.

A salt-tolerant strain, Pseudomonas mendocina A4, was isolated from brackish-water ponds showing simultaneous heterotrophic nitrification-aerobic denitrification and phosphorus removal capability. The optimal conditions for nitrogen and phosphate removal of strain A4 were pH 7-8, carbon/nitrogen ratio 10, phosphorus/nitrogen ratio 0.2, temperature 30 °C, and salinity range of 0-5 % using sodium succinate as the carbon source. The nitrogen and phosphate removal efficiencies were 96-100 % and 88-96 % within 24 h, respectively. The nitrogen and phosphate removal processes were matched with the modified Gompertz model, and the underlying mechanisms were confirmed by the activities of key metabolic enzymes. Under 10 % salinity, the immobilization technology was employed to enhance the nitrogen and phosphate removal efficiencies of strain A4, achieving 87 % and 76 %, respectively. These findings highlight the potential application of strain A4 in both freshwater and marine culture wastewater treatment.

Simultaneous inorganic nitrogen and phosphate removal by aerobic-heterotrophic fungus Fusarium keratoplasticum FSP1: Performance, pathway and application.

Fungi with multiple contaminant removal function have rarely been studied. Here, a novel fungal strain Fusarium keratoplasticum FSP1, which was isolated from halophilic granular sludge, is reported for first time to perform simultaneous nitrogen and phosphate removal. The strain showed wide adaptability under C/N ratios of 30-35, salinities of 0 %-3 % (m/v), and pH of 7.5-9.5. The maximum removal rates of ammonium, nitrate and nitrite were 4.43, 4.01 and 2.97 mg N/L/h. The nitrogen balance, enzyme activity and substrate conversion experiments demonstrated a single strain FSP1 can assimilate inorganic nitrogen and convert inorganic nitrogen to gaseous nitrogen through heterotrophic nitrification or aerobic denitrification. About 39 %-42 % of the degraded phosphorus was in the extracellular polymeric substances (EPS). Orthophosphate was the main phosphorus species in the cell, whereas phosphate monoester and diester were in the EPS. The novel strain FSP1 is a potential candidate for wastewater treatment.

Microalgae-assisted heterotrophic nitrification-aerobic denitrification process for cost-effective nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and bacterial community.

A microalgae-assisted heterotrophic nitrification-aerobic denitrification (HNAD) system for efficient nutrient removal from high-salinity wastewater was constructed for the first time as a cost-effective process in the present study. Excellent nutrient removal (∼100.0 %) was achieved through the symbiotic system. The biological removal process, biologically induced phosphate precipitation (BIPP), microalgae uptake, and ammonia stripping worked together for nutrient removal. Furthermore, the biological removal process achieved by biofilm contributed to approximately 55.3-71.8 % of nitrogen removal. BIPP undertook approximately 45.6-51.8 % of phosphorus removal. Batch activity tests confirmed that HNAD fulfilled an extremely critical role in nitrogen removal. Microalgal metabolism drove BIPP to achieve efficient phosphorus removal. Moreover, as the main HNAD bacteria, OLB13 and Thauera were enriched. The preliminary energy flow analysis demonstrated that the symbiotic system could achieve energy neutrality, theoretically. The findings provide novel insights into strategies of low-carbon and efficient nutrient removal from high-salinity wastewater.

Heterotrophic growth of Galdieria sulphuraria on residues from aquaculture and fish processing industries.

The study aimed at zero-waste utilization of fish processing streams for cultivation of microalgae Galdieria sulphuraria. Wastewater from a fish processing facility, slam (mix of used fish feed and faeces), and dried pellet (sediments after enzymatic hydrolysis of rainbow trout) were investigated as potential sources of carbon, nitrogen, and phosphate for cultivation of G. sulphuraria. The pellet extract was found to support the growth of G. sulphuraria when appropriate diluted, at concentrations below 40 % (v/v). It was revealed that wastewater does not impact the growth negatively, however free amino nitrogen and carbon sources need to be supplied from another source. Therefore, only proteolyzed pellet extract (20 %, v/v) was selected for upscaling and a biomass concentration of 80 g L-1 (growth rate was 0.72 day-1) was achieved in a non-sterile fed-batch culture. Even though biomass was produced under non-sterile conditions no pathogens such as Salmonella sp. could be detected.

Optimizing heterotrophic nitrification process: The significance of demand-driven aeration and organic matter concentration.

Heterotrophic nitrification and aerobic denitrification (HNAD) sludge were successfully acclimated. The effects of organics and dissolved oxygen (DO) on nitrogen and phosphorus removal by the HNAD sludge were investigated. The nitrogen can be heterotrophically nitrified and denitrified in the sludge at a DO of 6 mg/L. The TOC/N (total organic carbon to nitrogen) ratio of 3 was found to result in removal efficiencies of over 88% for nitrogen and 99% for phosphorus. The use of demand-driven aeration with a TOC/N ratio of 1.7 improved nitrogen and phosphorus removal from 35.68% and 48.17% to 68% and 93%, respectively. The kinetics analysis generated an empirical formula, Ammonia oxidation rate = 0.08917·(TOC·Ammonia)0.329·Biomass0.342. The nitrogen, carbon, glycogen, and poly-ß-hydroxybutyric acid (PHB) metabolism pathways of HNAD sludge were constructed using the Kyoto Encyclopedia of Genes and Genomes (KEGG). The findings suggest that heterotrophic nitrification precedes aerobic denitrification, glycogen synthesis, and PHB synthesis.

Enhanced efficiency and mechanism of low-temperature biochar on simultaneous removal of nitrogen and phosphorus by combined heterotrophic nitrification-aerobic denitrification bacteria.

In this study, three strains of heterotrophic nitrification-aerobic denitrification (HN-AD) capable of simultaneously removing phosphorus were isolated from activated sludge, and low-temperature coconut shell biochar was prepared. The metabolic effects of combined HN-AD bacteria on the total nitrogen (TN) and total phosphorus (TP) were investigated, and the enhanced efficiency and mechanism of low-temperature biochar on the combined bacteria were also explored. The results indicated that the combined bacteria could adapt to environmental impacts and multiple nitrogen sources. The low-temperature biochar containing more aliphatic carbon and oxygen-containing functional groups enhanced the metabolic activity of combined HN-AD bacteria and accelerated the electron transfer process during nitrogen and phosphorus degradation. The removal efficiencies of TN and TP increased by 68% and 88%, respectively, in the treatment of actual sewage by biochar attached with combined bacteria. The findings form a basis for the engineering utilization of HN-AD and are of great practical significance.

Treatment of nitrogen and phosphorus in wastewater by heterotrophic N- and P-starved microalgal cell.

Nitrogen (N) and phosphorus (P) are two major pollutants present in aquaculture wastewater, and their concentrations often do not meet discharge standards. In the present study, the N and P removal efficiency of nutrient-deficient cells (S group) was significantly higher than that of photoautotrophic cells (P group) and heterotrophic cells (H group). After incubation with wastewater, the N and P content of S group cells was significantly increased and reached a level similar to that of the P group and H group cells after 6 days of treatment. Additionally, in the S group cells, the content of total fatty acids (TFAs), which can be used to supply energy and organic carbon for N and P absorption, significantly decreased. In addition, the protein and nucleic acid contents of the S group cells also significantly increased, which revealed the biosynthetic flow of assimilated N and P. Comparative transcriptome analysis showed that compared with the P group and H group, the N metabolism, ribosome, RNA polymerase, and fatty acid degradation pathways were significantly upregulated in the S group cells, and the fatty acid biosynthesis pathway was significantly downregulated, which was in agreement with the biochemical results. In summary, our study showed that N- and P-starved heterotrophic cells are ideal for use in wastewater N and P removal processes. Keypoints • The N and P removal efficiencies of the S group were higher than P and H groups • Fatty acids were degraded to supply energy and carbon for N and P absorption • N metabolism and fatty acid degradation pathways were upregulated in the S group.

Simultaneous bioremediation of Disperse orange-2RL Azo dye and fatty acids production by Scenedesmus obliquus cultured under mixotrophic and heterotrophic conditions.

Several types of green photosynthetic microalgae can grow through the process of heterotrophic growth in the dark with the help of a carbon source instead of the usual light energy. Heterotrophic growth overcomes important limitations in the production of valuable products from microalgae, such as the reliance on light, which complicates the process, raises costs, and lowers the yield of potentially useful products. The present study was conducted to explore the potential growth of green microalga Scenedesmus obliquus under mixotrophic and heterotrophic conditions utilizing Disperse orange 2RL Azo dye as a carbon source to produce a high lipid content and the maximum dye removal percentage. After 7 days of algal growth with dye under mixotrophic and heterotrophic conditions with varying pH levels (5, 7, 9, and 11), KNO3 concentrations (1, 1.5, 2, and 3 g/L), and dye concentrations (20, 40, and 60 ppm); dye removal percentage, algal dry weight, and lipid content were determined. The results showed that the highest decolorization of Disperse orange 2RL Azo dye (98.14%) was attained by S. obliquus in heterotrophic medium supplemented with glucose at the optimal pH 11 when the nitrogen concentration was 1 g/L and the dye concentration was 20 ppm. FT-IR spectroscopy of the dye revealed differences in peaks position and intensity before and after algal treatment. S. obliquus has a high concentration of oleic acid, which is enhanced when it is grown with Disperse orange 2RL Azo dye, making it ideal for production of high-quality biodiesel. In general, and in the vast majority of instances, heterotrophic cultivation is substantially less expensive, easier to set up, and requires less maintenance than mixotrophic cultivation. Heterotrophic cultivation allows for large-scale applications such as separate or mixed wastewater treatment along with biofuel production.

Simultaneous removal of organic matter and nitrogen by heterotrophic nitrification-aerobic denitrification bacteria in an air-lift multi-stage circulating integrated bioreactor.

This study aimed to propose a novel air-lift multi-stage circulating integrated bioreactor (AMCIB) to treat urban sewage. The AMCIB combined the reaction zone and sedimentation zone, the alternating circulation of activated sludge in separate aerobic and anaerobic environments facilitates the enrichment of HN-AD bacteria. The preliminary study showed that AMCIB had high removal efficiencies for COD, NH4+-N, TN and TP under high dissolved oxygen (DO) concentration conditions, with average removal rates of 93.21 %, 96.04 %, 75.06 % and 94.30 %, respectively. IlluminaMiSeq sequencing results showed that the system successfully cultured heterotrophic nitrification-aerobic denitrification (HN-AD) functional bacteria (Pseudomonas, Acinetobacter, Aeromonas) that played a crucial role in sewage treatment, and Tetrasphaera was the central phosphorus removing bacteria in the system. Functional gene predictions showed that the HN-AD played a dominant role in the system.

Synchronous removal of ammonia nitrogen, phosphate, and calcium by heterotrophic nitrifying strain Pseudomonas sp. Y1 based on microbial induced calcium precipitation.

Pseudomonas sp. Y1, a strain with superior synchronous removal ability of ammonia nitrogen (NH4+-N), phosphate (PO43--P), and calcium (Ca2+) was isolated, with the removal efficiencies of 92.04, 99.98, and 83.40 %, respectively. Meanwhile, the chemical oxygen demand (COD) was degraded by 90.33 %. Through kinetic analysis, the optimal cultivated conditions for heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization were determined. The growth curves experimental results of different nitrogen sources indicated that strain Y1 could remove NH4+-N through HNAD. The results of excitation-emission matrix (EEM) proved that the appearance of extracellular polymeric substances (EPS) promoted the precipitation of phosphate minerals. Finally, the characterization results of the bioprecipitates showed that the HNAD process produced the alkalinity required for microbial induced calcium precipitation (MICP), resulting in the removal of PO43- via adsorption and co-precipitation. This study provides a theoretical basis for the application of microorganisms to achieve synchronous nutrient removal and phosphorus recovery in wastewater.

Nitrogen removal intensification of aerobic granular sludge through bioaugmentation with "heterotrophic nitrification-aerobic denitrification" consortium during petroleum wastewater treatment.

The bioaugmentation potential of aerobic granular sludge (AGS) was investigated using heterotrophic nitrification-aerobic denitrification (HN-AD) bacterial consortium to improve nitrogen removal during petroleum wastewater treatment. An efficient HN-AD consortium was constructed by mixing Pseudomonas mendocina K0, Brucella sp. K1, Pseudomonas putida T4 and Paracoccus sp. T9. AGS bioaugmented by immobilized HN-AD consortium enhanced nitrogen removal, which showed NH4+-N and TN removal efficiency of 92.4% and 79.8%, respectively. The immobilized consortium addition facilitated larger AGS formation, while granules > 2.0 mm accounted for 16.7% higher than that of control (6.7%). Further, the abundance of napA gene was 4-times higher in the bioaugmented AGS as compared to the control, which demonstrated the long-term stability of HN-AD consortium in the bioreactor. The bioaugmented AGS also showed a higher abundance of xenobiotics biodegradation and nitrogen metabolism. These results highlight that bioaugmentation of AGS technology could be effectively used for enhanced denitrification of petroleum wastewater.

[Effects of directional adaptation on selenium tolerance and accumulation of heterotrophic Chlorella pyrenoidosa].

Selenium (Se) is an essential trace element for organisms. Se deficiency will cause diseases such as Keshan disease and Kashin-Beck in human being, and huge loss to animal husbandry. Currently available Se supplements have such problems as low Se content, poor bioavailability, and poor safety. Chlorella pyrenoidosa can produce bioavailable and safe organic Se under suitable conditions, which is thus a promising Se supplement. Therefore, in this study, we tried to improve the Se tolerance and accumulation of C. pyrenoidosa by directional adaptation. To be specific, we gradually increased the concentration of Na2SeO3 in medium to domesticate C. pyrenoidosa and optimized the adapting time and concentration gradient of Na2SeO3 during the adaptation. The results showed that the adapted C. pyrenoidosa was more tolerant to Se and had stronger Se enrichment ability. In 5 L fermenter, the adapted strains could tolerate 40 mg/L Na2SeO3 and the synthesis rate of organic Se was 175.6% higher. Then, Se addition method in the 5 L fermenter was optimized. The result demonstrated that addition of Na2SeO3 at 40 mg/L during heterotrophic culture achieved the final dry weight of C. pyrenoidosa cells at 106.4 g/L, content of organic Se at 1 227 mg/kg, and synthesis rate of organic Se at 1.36 mg/(L·h). Compared with the reported highest cell density of 75 g/L and the highest organic Se content of 560 mg/kg, the corresponding figures in this study were 41.9% and 119.1% higher, respectively. In conclusion, directional adaptation can remarkably improve the Se tolerance and enrichment of C. pyrenoidosa.

Effects of directional adaptation on selenium tolerance and accumulation of heterotrophic Chlorella pyrenoidosa / 生物工程学报

Selenium (Se) is an essential trace element for organisms. Se deficiency will cause diseases such as Keshan disease and Kashin-Beck in human being, and huge loss to animal husbandry. Currently available Se supplements have such problems as low Se content, poor bioavailability, and poor safety. Chlorella pyrenoidosa can produce bioavailable and safe organic Se under suitable conditions, which is thus a promising Se supplement. Therefore, in this study, we tried to improve the Se tolerance and accumulation of C. pyrenoidosa by directional adaptation. To be specific, we gradually increased the concentration of Na2SeO3 in medium to domesticate C. pyrenoidosa and optimized the adapting time and concentration gradient of Na2SeO3 during the adaptation. The results showed that the adapted C. pyrenoidosa was more tolerant to Se and had stronger Se enrichment ability. In 5 L fermenter, the adapted strains could tolerate 40 mg/L Na2SeO3 and the synthesis rate of organic Se was 175.6% higher. Then, Se addition method in the 5 L fermenter was optimized. The result demonstrated that addition of Na2SeO3 at 40 mg/L during heterotrophic culture achieved the final dry weight of C. pyrenoidosa cells at 106.4 g/L, content of organic Se at 1 227 mg/kg, and synthesis rate of organic Se at 1.36 mg/(L·h). Compared with the reported highest cell density of 75 g/L and the highest organic Se content of 560 mg/kg, the corresponding figures in this study were 41.9% and 119.1% higher, respectively. In conclusion, directional adaptation can remarkably improve the Se tolerance and enrichment of C. pyrenoidosa.

Phosphorus uptake, distribution and transformation with Chlorella vulgaris under different trophic modes.

Phosphorus (P) uptake, distribution and transformation are important processes associated with the growth and metabolism of microalgae. In this study, the fate of P in soluble microbial products (SMP), extracellular polymeric substances (EPS), and intracellular polymeric substances (IPS) of Chlorella vulgaris C7 in the form of inorganic P (IP) and organic P (OP) was studied under different trophic modes, including photoautotrophy, heterotrophy and mixotrophy. The results showed that mixotrophic cultivation of microalgae brought highest biomass yield, which was 2.09 times and 11.10 times higher than that of the photoautotrophic and heterotrophic conditions. Regarding P distribution and transformation, the trophic modes affected the transformation trends and rates of P in the form of IP and OP among SMP, EPS and IPS. Under photoautotrophic condition, EPS was the main P pool, and most of P in C. vulgaris was IP. While, under mixotrophic condition, IPS was the main P pool, and most of P was transformed to OP. The addition of glucose promoted the uptake of P by algal cells and the transformation of IP to OP, which accounted for 79.32% of total phosphorus at the end of cultivation. Collectively, mixotrophic cultivation was regarded as the optimum approach for microalgae cultivation and nutrient recovery.

Marine macroalga-associated heterotroph Bacillus velezensis as prospective therapeutic agent.

Marine macroalgae and their accompanying microbial flora were proved to be the reservoir of potential bioactive compounds with promising pharmacological applications. Heterotrophic bacteria concomitant with the marine algae were isolated and screened for their antibacterial potential against clinically recognized pathogens. The bacterial isolate with greater bioactive properties was identified as Bacillus velezensis MBTDLP1 (phylum Firmicutes), which was isolated from the marine macroalga Laurencia papillosa, by integrated morphological, biochemical and molecular characterization. B. velezensis showed promising antibacterial property against methicillin-resistant Staphylococcus aureus and Vibrio parahemolyticus with inhibition zone of 32-36 mm. Organic ethyl acetate extract of the isolate also displayed prospective antibacterial activity against the test pathogens (minimum inhibitory concentration 7.5-15 µg/mL), coupled with promising antioxidant (IC50 0.1-0.9 mg/mL against oxidants), anti-inflammatory (IC50 0.01 mg/mL against 5-lipoxygenase), and carbolytic enzyme attenuation properties (IC50 0.1-0.4 mg/mL in response to α-amylase and α-glucosidase). Significant anticancer potential against breast carcinoma (MCF-7) cells (IC50 0.03 mg/mL) coupled with lesser cytotoxicity to the normal fibroblast (3T3L) cells (IC50 0.14 mg/mL) were also recognized. The apoptosis assay could give reasonable outcome as the organic extract of B. velezensis induced apoptosis to 81% of the cancer cells while maintaining almost 60% viability in normal cells. The results put forward that B. velezensis MBTDLP1 could be used to isolate bioactive compounds with therapeutic potential and biomedical applications.

Biological nitrogen and phosphorus removal by a phosphorus-accumulating bacteria Acinetobacter sp. strain C-13 with the ability of heterotrophic nitrification-aerobic denitrification.

Strain C-13, identified as an Acinetobacter sp. by homology searches, exhibited efficient simultaneous heterotrophic nitrification-aerobic denitrification phosphorus removal (SNDPR) abilities by nitrogen balance analysis and further confirmation of successful amplification of functional genes ppk, napA, and nirS. In addition, strain C-13 could utilize NH4+-N, NO3--N, and NO2--N as nitrogen sources, among which NH4+-N was indicated to be an excellent nitrogen source for assimilation and heterotrophic nitrification. Besides, the optimum conditions for nutrient removal were determined as follows: sodium acetate as the sole carbon source, C/N/P ratio of 100/10/2, pH = 7.5, and temperature of 30 °C. Meanwhile, the strain also showed the traditional features, such as release and the excess uptake of phosphate under anaerobic/aerobic conditions, with the highest phosphorus content of 5.01% after cultivation. Strain C-13 presents promising prospects for application in biologicalnutrient removal in wastewater treatment.

Stepwise treatment of undiluted raw piggery wastewater, using three microalgal species adapted to high ammonia.

A high ammonia concentration and chemical oxygen demand (COD) in piggery wastewater force it to be diluted before conventional microalgal treatment to reduce ammonia toxicity. Incomplete treatment of ammonia and COD in piggery wastewater may cause eutrophication, resulting in algal blooms. This study tried to treat raw piggery wastewater without dilution, using three strains of microalgae (Chlorella sorokiniana, Coelastrella sp. and Acutodesmus nygaardii) that outcompeted other algae under heterotrophic, mixotrophic, and autotrophic conditions, respectively, through adaptive evolution at high ammonia concentration. The three stepwise processes were designed to remove (1) small particles, COD, and phosphorus in the 1st heterotrophic C. sorokiniana cultivation, (2) ammonia and COD in the 2nd mixotrophic Coelastrella sp. cultivation, and (3) the remaining ammonia in the 3rd photoautotrophic A. nygaardii cultivation. To enhance ammonia uptake rate, each algal species were inoculated after 2-day nitrogen starvation. When the N-starved three species were inoculated at each step sequentially at 7 g/L for 2 days, the final phosphorus, COD, and ammonia removal efficiencies were 100% (16.4-0 mg/L), 92% (6820-545 mg/L), 90% (850-81 mg/L) and turbidity (99%) after total 6 days.

Simultaneous nitrification-denitrification by phosphate accumulating microorganisms.

Nitrogen and phosphorous are important inorganic water pollutants that pose a major threat to the environment and health of both humans and animals. The physical and chemical ways to remove these pollutants from water and soil are expensive and harsh, so biological removal becomes the method of choice to alleviate the problem without any side effects. The identification of microorganisms capable of simultaneous heterotrophic nitrification and aerobic denitrification has greatly simplified the sequestration of nitrogen from ammonium (NH4+) into dinitrogen (N2). Further, the discovery of phosphorous accumulating organisms offers greater economic benefits because these organisms can favourably and simultaneously remove both nitrogen and phosphorous from wastewaters hence reducing the nutrient burden. The stability of the system and removal efficiency of inorganic pollutants can be enhanced by the use of immobilized organisms. However, limited work has been done so far in this direction and there is a need to further the efforts towards refining process efficiency by testing low-cost substrates and diverse microbial populations for the total eradication of these contaminants from wastewaters.