Nutrient Removal Rates Research Articles

Application of Two Indigenous Strains of Microalgal Chlorella sorokiniana in Cassava Biogas Effluent Focusing on Growth Rate, Removal Kinetics, and Harvestability

Microalgae cultivation in wastewater is an emerging approach to remove its contaminants and generate microalgal biomass. This study aimed to screen and isolate potential strains in a cassava biogas effluent wastewater (CBEW) treatment system and produce algal biomass. Chlorella sorokiniana strains P21 and WB1DG were isolated from CBEW and found to grow by utilizing various carbon sources. Experiments conducted in a batch reactor using an unsterilized substrate were done to evaluate the nutrient removal and growth of isolated strains from CBEW. The results showed that C. sorokiniana P21 and WB1DG could achieve biomass accumulation of more than 2564 and 1301 mg L−1, respectively. The removal efficiencies of chemical oxygen demand (COD), total phosphorous (TP), and total inorganic nitrogen (TIN) were found up to be 63.42, 91.68, and 70.66%, respectively, in a WB1DG culture and 73.78, 92.11, and 67.33%, respectively, in a P21 culture. Harvestability of the P21 strain was examined using several coagulant–flocculants. FeCl3 was found to remove more than 90% of the cells. Nutrient removal and growth rates resulting from these indigenous strains with application of untreated CBEW support the possibility of this strain being a promising candidate to couple a CBEW treatment and algal biomass generation with minimal process adjustment.

Hortonian Scaling of Coupled Hydrological and Biogeochemical Responses Across an Intensively Managed River Basin

Structural and functional attributes across fractal river networks have been characterized by well-established and consistent hierarchical, Hortonian scaling patterns. In most of the global river basins, spatial patterns of human settlements also conform to similar hierarchical scaling. However, emergent spatial hierarchical patterns and scaling of heterogeneous anthropogenic nutrient loads over a river basin are less known. As a case study, we examined here a large intensely managed river basin in Germany (Weser River; 46K km2; 8M population). Archived data for point-/diffuse-sources of total Phosphorus (Ptot) input loads were combined with numerical and analytical model simulations of coupled hydrological and biogeochemical processes for in-stream Ptot removal at the network scale. We find that Ptot input loads scale exponentially over stream-orders, with the larger scaling constant for point-source loads from urban agglomerations compared to those for diffuse-source contributions from agricultural and forested areas. These differences in scaling patterns result from hierarchical self-organization of human settlements, and the associated clustering of large-scale, altered land-cover. Fraction of Ptot loads removed through in-stream biogeochemical processes also manifests Hortonian scaling, consistent with predictions of an analytical model. Our analyses show that while smaller streams are more efficient in Ptot removal, in larger streams the magnitude of Ptot loads removed is higher. These trends are consistent with inverse scaling of nutrient removal rate constant with mean discharge, and downstream clustering of larger cumulative input loads. Analyses of six nested sub-basins within the Weser River Basin also reveal similar scaling patterns. Our findings are useful for projecting likely water-quality spatial patterns in similar river basins in Germany, and Central Europe. Extensions and generalizations require further examination of diverse basins with archetype spatial heterogeneities in anthropogenic pressures and hydroclimatic settings.

The potential of different marine microalgae species to recycle nutrients from recirculating aquaculture systems (RAS) fish farms and produce feed additives

This study researched the use of six microalgae species (N. gaditana, P. lutheri, I. galbana, T. chuii, P. tricornutum and C. gracilis) and a bloom to treat effluent from a marine fish farm and produce quality biomass. More specifically, simulated water from a recirculating aquaculture system (RAS) was used. Microalgae culture was carried out under controlled conditions using 18 L bubble column photoreactors under batch and semi-continuous operation. The main parameters analysed were micronutritional requirements, biomass productivity, nutrient removal rate (nitrogen and phosphorus), biomass composition, and quality. Also, based on the results obtained, a quantitative classification of the microalgae was carried out. The results showed that all microalgae required at least trace metals. In certain species, the addition of vitamins was also required for viable cultivation. In the case of biomass productivity under batch operation, values were between 67 mg L−1 d−1 and 7 mg L−1 d−1 using T. chuii and C. gracilis, respectively, and between 71 mg L−1 d−1 and 9 mg L−1 d−1 using T. chuii and N. gaditana under semi-continuous operation. In the case of total dissolved phosphorus removal, no differences were found between species, reaching in all cases final concentrations <0.01 mg L−1. Total dissolved nitrogen removal rate varied between species and operating conditions, being the highest obtained using T. chuii under semi-continuous operation (12.6 mg L−1 d−1) and the lowest with C. gracilis batch operation (0.15 mg L−1 d−1). Biomass composition in terms of protein and lipids varied between species and operating conditions, but quality in terms of amino acids and fatty acids profile remained homogeneous in all cases. Finally, according to the developed score methodology, I. galbana was the microalgae with the highest biomass production score, while T. chuii was for wastewater treatment.

Viability assessment of algal wastewater treatment projects under outdoor conditions based on algal productivity and nutrient removal rate

In this work, a viability study of algal wastewater treatment projects under outdoor conditions is proposed. The viability analysis of solar plant projects based on annual exceedance probability, which is the probability that a certain energy value will be exceeded, is applied. The two outputs used (algal productivity and ammonium uptake rate) are obtained from literature models under different scenarios. The first scenario studies algal productivity of the microalgae Chlorella vulgaris cultivation in an open pond system. The second scenario considers the ammonium uptake rate of the microalgae Scenedesmus sp. Cultivation in a flat-plate photobioreactor. Both scenarios are set out under outdoor conditions in two stations with different climates.The work also aims at including in the viability study an analysis of the intermittency of productivity/ammonium uptake rate to take into account intra-annual variability. The study of variability is usually limited to the estimation of statistics during each season. The methodology proposed, based on exceedance probabilities of variation, evaluates discontinuities in the production and/or nutrient removal processes.Finally, the work aims at evaluating the effects of storage on the discontinuities that can compromise project viability defining the Risk Factor Improvement Index. This index assesses the degree of improvement in viability due to discontinuity in productivity and ammonium removal processes provided by storage. According to this index, improvements of up to 31% for the productivity and up to 20% for the ammonium uptake rate can be reached. By including storage, the discontinuity effect and thus the intermittency analysis may be disregarded.

Assessment the ability of Trichoderma harzianum Fungi in Bioremediation of some of Heavy Metals in Waste Water

The study included the use of Trichoderma harzianum for biodegradation heavy metals in a wastewater treatment plant and their ability to decompose these minerals through a series of tests. The first test involved the use of two Trichoderma harzianum isolates for biodegradation through a filtration action. In the second test, the comparison was used in pre and post-treatment in Petri dishes, The result showed a clear green growth of fungi and their use of heavy metals as an energy source. Scanning Electronic Microscope SEM) was used to compare the vegetative growth of fungi before and after treatment on P.D.A media, which showed clear and normal growth with a short growth period of the Petri dish after treatment and compared it to the control of the Petri dish with different magnification powers (6738x, 5988x, 2713x, 2509x)., 6453x, 5708x, 2598x, 2400x). A third test used a Atomic Absorption technique to quantify heavy metals for the site 2 after 28 days of bioremediation. The results showed the highest removal rate of Cd was 98.63% and Mn was94.35% for (T.h1) and the lowest biodegradation of Zn and Fe (39.77% and 47.43%,) respectively. The nutrient had the highest removal rate of PO4 was 69.87% and the lowest percentage of NO3 was 8.91%.The results also showed the highest removal rate for (T.h2) Mn and Cd with rates of 86.41% and 81.73%, the lowest percentage of decomposition of Zn was 52.27%, and the highest percentage of decomposition of PO4 was 70.74% Lowest removal rate of NO3 was 36.49%. A Atomic Absorption technique was used to quantify heavy metals after 28 days of biological treatment for the site1. The results showed the highest biodegradation percentage (T.h1) for manganese and Pb 83.27% and 84.50%, respectively, and the lowest biodegradation percentage was Zn and Fe (33.67%, 38.09%,) respectively, and the nutrient removal rate was the highest, NO3 was 85.27 %, The lowest rate is 27.74% of SO4. The results showed the highest removal rate (T.h2) for the elemental fungus Mn (87.32%) and Pb (84.01%) and the lowest percentage for Fe was (36.90%).The results of the experiment showed that the fungi largest biomass are the most efficient in the bioremediation process and the removal of pollutants from wastewater.

Long-term performance and microbial mechanism in intertidal wetland sediment introduced constructed wetlands treating saline wastewater

Saline wastewater requires a clean and efficient treatment method to avoid frequent public health events and nonpoint source pollution. This study explored intertidal wetland sediment (IWS) as an inoculation source for long-term operation in saline constructed wetlands (CWs). Four CWs planted with Phragmites australis were set up. In two of them, IWS was introduced for saline wastewater treatment (150 mg/L NaCl) and salt-free treatment; and set other CWs as control groups. Nutrient removal rates, microbial community, and functional genus were detected in IWS-introduced CWs and control CWs over three years. The average removal rates of total phosphorus and chemical oxygen demand were 17.37% and 20.35% higher, respectively, in IWS-introduced CWs than in control CWs under a salty environment. No significant difference in NH4+–N removal was observed among all treatments (p > 0.05), and the removal rates in all treatments were above 90%. Results showed that IWS-introduced CWs achieved high levels of halophilic bacteria (Proteobacteria), denitrifying bacteria (Actinobacteria, Gammaproteobacteria), and anaerobic phosphate-accumulating organisms (PAOs) (Alphaproteobacteria, Anaerolineae) in the substrate. The bacterial community of the rhizosphere was dominated by “Pseudonocardiaceae,” “Rhodobacteraceae,” and “Rhizobiaceae” in the IWS-introduced CWs, known as COD-removing bacteria and aerobic PAOs. These bacteria chronically enhanced the pollutant removal performance, salt tolerance, and operational stability of CWs in three years. Overall, microbial augmentation through the IWS as an inoculation source in CWs is effective and has potential in long-term saline wastewater treatment.

Enhanced removal of antibiotics and decreased antibiotic resistance genes in the photo-sequencing batch reactor during the aquaculture wastewater treatment

ABSTRACT The performance of photo-sequencing batch reactor (PSBR) in removing multiple antibiotics and nutrients from aquaculture wastewater as well as the antibiotic resistance genes (ARGs) proliferation were firstly investigated during the long-term experiments. The operational conditions (i.e. light intensity, light time, aeration and solid retention time) were optimised to realise the simultaneous removal of antibiotics and nutrients. It was found that, compared with traditional SBR, PSBR has similar nutrient removal rate and a 30% higher antibiotics removal rate due to the corporation of microalgae (Chlorella) and bacteria, and the absolute abundance of ARGs decreased by 78% in PSBR. Further investigation showed that PSBR had certain advantages in removing quinolones and the corresponding removal rate could reach up to 90%. In terms of the mechanisms, the possible metabolic pathway of antibiotic was analysed and the intermediate metabolites were different from that of the reported studies. The microbial communities were also affected by microalgae and the relative abundance of certain bacteria (such as members of the families Rhodocyclaceae and Burkholderiaceae), which were positively correlated with some ARGs, decreased in PSBR. This study provides an alternative and effective method to aquaculture wastewater treatment, which present high nutrients and antibiotics removal efficiencies and low ARGs transmission.

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

CIP wastewater is one of the major wastewater streams from the food industry, and its treatment is generally expensive, requiring a large effort to reduce its typically high nitrogen (N), and phosphorus (P) contents. Microalgae-based wastewater treatment is increasingly explored as a more sustainable alternative to the conventional methods, due to the added benefit of nutrient upcycling and value-added biomass production. For the first time, four microalgae species were used to treat CIP wastewater high in N (565.5 mg NO3−-N/l) and P (98.0 mg PO43−-P/l). An intermittent biomass harvesting strategy was adopted in this study to enhance the purification of CIP water and redirection of nutrients into algal biomass. Over 93 days operation, N removal efficiency was 52.1 ± 2.9%, 54.8 ± 2.5%, 50.0 ± 2.3% and 48.3 ± 0.5%, and P removal efficiency was 65.5 ± 10.0%, 79.4 ± 6.1%, 61.8 ± 2.5% and 69.1 ± 7.7% for Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus obliquus and wastewater borne microalgae, respectively. After the first (acclimatization) and second growth cycles, cell growth and nutrient removal slowed down but increased again after adding trace nutrients, indicating the lack of trace elements after the first two growth cycles. In the fourth and fifth batch runs, both algal growth rate and nutrient removal rate decreased despite adding trace nutrients and/or increasing light intensity, this being a consequence of the excreted soluble algal products accumulating during long-term operation. S. obliquus had the highest protein concentration of 44.5 ± 9.8% DW, while C. vulgaris accumulated the highest total lipid content (15.6 ± 0.9%, DW). In this proof-of-concept study, the cultivation of microalgae in CIP wastewater with an intermittent harvest of the accumulated algal biomass is demonstrated and it outlines the potential of microalgae to sustainably treat effluents with extremely high nutrients concentration while producing the food-grade algae biomass.

Growth and bioactivity of two chlorophyte (Chlorella and Scenedesmus) strains co-cultured outdoors in two different thin-layer units using municipal wastewater as a nutrient source

The application of microalgae in wastewater treatment has recently been at the forefront of interest due to the increasing concern about environmental protection and economic sustainability. This work aimed to study two chlorophyte species, Chlorella vulgaris and Scenedesmus acutus, co-cultured outdoors in centrate of municipal wastewater as a nutrient source. Two different thin-layer units were used in these trials — thin-layer cascade (TLC) and thin-layer raceway pond (TL-RWP), suitable for this purpose due to their high biomass productivity and better culture transparency when using muddy wastewater. The units were operated in batch, and subsequently in semi-continuous growth regime — and monitored in terms of photosynthetic performance, growth, nutrient removal rate, and bioactivity. The results showed that the co-cultures grew well in the centrate, achieving the maximum biomass densities of 1.3 and 2.1 g DW L−1 in TLC and TL-RWP, respectively, by the end of the batch regime and 1.9 and 2.0 g DW L−1 by the end of the semi-continuous regime. Although TL-RWP grown cultures showed faster growth, the TLC-one revealed better nutrient removal efficiencies batch wise than the culture grown in TL-RWP — removing up to 48% of total nitrogen and 43% of total phosphorus. Conversely, the latter was more efficient under the semi-continuous regime (54% and 42% consumption of total nitrogen and phosphorus, respectively). In the harvested biomass, an important antimicrobial activity (specifically antifungal) was detected. In this sense, the in-vitro growth of the oomycete Pythium ultimum was inhibited by up to 45% with regard to the control. However, no biostimulating activity was observed. The present findings confirm the possibility of using these two species for biomass production in municipal wastewater centrate using highly productive thin-layer systems. This technology can be a valuable contribution to circular economy since the produced biomass can be re-applied for agricultural purposes.

Effects of root exudates on rhizosphere bacteria and nutrient removal in pond-ditch circulation systems (PDCSs) for rural wastewater treatment

Pond-ditch circulation system (PDCS) is a promising remediation strategy for rural wastewater treatment. Aquatic plants play nonnegligible roles in the nutrient removal of the PDCS. However, mechanisms of root exudates regulating nutrient removal in PDCSs remained unclear. In our study, the PDCS achieved higher total nitrogen (TN) and phosphorus (TP) removal rates (72.7–97.4%) compared to the static system. Protein contents in root exudates of the PDCS ranged from 0.041 to 1.332 mg L−1, showing negative associations with Simpson index. Lactic acid and tartaric acid in the PDCS varied from 0.045 to 0.380 mg L−1 and 0.024 to 5.446 mg L−1, which were tightly linked with TN, TP, and TP removal rates and most sediment properties, especially sediment total nitrogen (STN) and total organic carbon (TOC), and sediment inorganic phosphorus (SIP). Moreover, the top 3 relative dominant genus were Bacillus (0.11%–17.90%), Geobacter (0.35%–12.04%), and Clostridium sensu stricto 1 (0.14%–12.05%), which might be the predominant groups in nutrient removal of PDCSs. RDA results indicated that lactic acid, protein, and amino acids were positively correlated with Geobacter; while Bacillus was significantly affected by water content. Path analysis further demonstrated that the indirect effect of secretion from plant roots on nutrient removal rates was mainly through modulating bacteria diversity and relative abundance. Taken together, root exudates, especially protein, amino acids, and lactic acid, altered rhizosphere microbial relative abundance and diversity, where the impacts were bacterial species-dependent.

Large-scale hybrid accidental urban wetland for polluted river purification in northern China: Evidence and implications for urban river management

Hybrid accidental urban wetlands (HAUWs) are expected to be a potential low-cost and highly efficient alternative means of minimizing pollutant loads from municipal areas as compared to the single-stage system being used. These unexpected HAUWs are created not through deliberate restoration, but as a result of water infrastructure decisions by local government. However, information on the long-term purification efficiency of large-scale HAUW improving eutrophic urban rivers is largely unexplored. An in-situ HAUW system consisting of a rubber dam, detention pond, accidental urban wetland, and overflow weir was evaluated at the field-scale for the purification of a eutrophic urban river in Zhangjiakou City, Hebei Province. The results for seven months of operation demonstrated that the effluent TP and NH4-N in the HAUW system could comply with the Grade III of Chinese National Surface Water Quality Standards. Average removal efficiencies for TN, NH4-N, NO3-N, TP, and PO4-P in the summer–autumn period of 52.6, 65,8, 56.6, 51.4, 58.2 and 88.3%, respectively, were recorded. These removal efficiencies were 59.4, 61.5, 65.6, 57.1, 59.4 and 65.7% higher than the respective values in the spring period. Furthermore, removal rates of nutrients were highly sensitive to temperature and showed seasonal trends. Further analysis showed that, with the application of the HAUW system, a total of 92.1, 69.5, 57.3, 37.8, 33.2, 12.4, 14.5, 7.3, 3.4% removal of Al, Mn, Cd, Pb, Zn, Ni, Fe, Ni, and As was achieved. Mean removal rates of TN, NH4-N, NO3-N, TP, TDP, PO4-P in the summer–autumn period were 2- 5 times higher than in those recorded in the early spring period. These results suggest that a variety of contaminant elimination mechanisms were offered by the HAUW, including enhanced hydraulic resistance, sedimentation, plant assimilation, microbial biofilm growth on roots’ surface and the HAUW design. Overall, this study demonstrated that the monitored HAUW could be another feature of the urban landscape that could help minimize pollutant loading to surface urban water bodies. This function is especially true in warm periods, in a similar way as natural wetlands or purposely built constructed wetlands. Nonetheless, managing these accidental treatment systems to maximize pollutant dissipation in the long-term would necessitate appropriate management strategies.

Full-scale vacuum degassing of activated sludge – A case study over 2-years of operation

The effect of vacuum degassing of activated sludge on biological wastewater treatment over a total period of 4 years was examined. In half of the period studied, the treatment system was classic, where wastewater, after a biological reactor with nitrification-denitrification and biological dephosphatation, was directed to secondary settlers. In the second period, the treatment system was modified so that the sludge from the biological reactor was directed to the vacuum degasser, followed by the secondary settling tanks (vacuum degassing activated sludge system; VDAS). As a result of using the VDAS, a significant improvement in sludge settling ability was recorded, which allowed the plant operators to increase the amount of biomass in the biological reactor. Differences in the quantity and quality of the wastewater influent were found during both periods. However, the quality of treated wastewater and the efficiencies of nutrient removal and removal rates were usually better in the system with vacuum degassing. An improvement was achieved not only for the elimination of the different forms of nitrogen, which by definition were to be removed as ammonia and gaseous nitrogen, but also for organic compounds expressed as COD and phosphorus. As a result of the lower sludge loading, sludge production expressed in g SS per g COD removed was significantly lower (20 %) with the VDAS.

Costs of mussel farming: A meta-regression analysis

Mussel farming has emerged as a relatively low-cost measure for reducing the content of nutrients in seas, but no systematic assessment has been undertaken of the costs involved. This study estimated the cost of producing mussels by means of a meta-regression analysis. The estimation of the cost function considered different types of mussel, environmental conditions and study characteristics. In total, 23 studies were found with a total of 69 observations. Different mixed-effect regression models were used and robust results were found of statistically significant output elasticities below one, i.e. production costs increase by less than 1% when the mussel quantity increases by 1%, and that the purpose of production, human consumption or nutrient removal, wage and interest rate and ecological conditions in terms of salinity level and temperature had significant effects on the costs. The estimated cost function was transferred to mussel farming for nutrient removal in different countries in the Baltic Sea, which indicated that the costs are relatively low for mussel farming in Russia (Kaliningrad).

Year-long performance assessment of an on-site pilot scale (100 L) photobioreactor on nutrient recovery and pathogen removal from urban wastewater using native microalgal consortium

The study was carried out as part of the Indo-Dutch collaboration project to ascertain the efficacy of the algal system for the treatment of urban wastewater. The study was done at Barapullah drain in New Delhi, using a pilot-scale (100 L) bubble column microalgae photobioreactor (PBR). The year-long study was intended to find the impact of seasonality coupled with varying hydraulic retention times (HRTs) on the PBR performance in terms of nutrient recovery, microbial contamination reduction, biomass productivity, and theoretical biomethane potential.To begin with, native microalgae consortium was enriched and cultivated in PBR directly on the Barapullah drain wastewater at the drain site. After achieving maximum recovery of nutrients in the batch mode, the PBR was operated in continuous mode at HRTs ranging from 1 to 3 days during summer, while 2–3 days during monsoon, autumn, and winter. The maximum and minimum biomass productivity obtained was 260 mg L−1 d−1 at the HRT of 1 day during summer and 77 mg L−1 d−1 at the HRT of 2 days during winter. At peak overall PBR performance at HRT of 2 days, the nutrient removal rate was 37.2 ± 6.2 mgCOD L−1 d−1, 39.3 ± 6 mgN L−1 d−1, and 4.7 ± 0.7 mgP L−1 d−1. Nearly 5 log removal of total and faecal coliform was obtained during summer and monsoon. However, the overall performance reduced during winters. The natural sedimentation of grown biomass achieved 81–95% of biomass settling at different HRTs. The areal footprint of the PBR is 1.42 m2 KLD−1, which was significantly lower than other pilot-scale microalgal wastewater treatment technologies. The obtained results at this lower HRT (2 days) even under non-optimized process parameters represent vital improvements over earlier reports with significantly higher HRTs. Results thus highlight the feasibility and scalability of the technology.

Soil exchangeable cations estimation using Vis-NIR spectroscopy in different depths: Effects of multiple calibration models and spiking

Due to high rate of nutrient removal by cotton plants, the productive cotton-growing soils of Australia are becoming depleted of exchangeable (exch.) cations. For long-term development, data on exch. calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na) throughout the soil profile is required. However, traditional laboratory analysis is tedious. The visible-near-infrared (Vis-NIR) spectroscopy is an alternative; whereby, spectral libraries are built which couple soil data and Vis-NIR spectra using models. While various models have been used to predict exch. cations, their performance was seldom systematically compared. Moreover, most previous studies have focused on prediction of topsoil (0–0.3 m) exch. cations while the effects of depth on applicability of topsoil spectral libraries are rarely investigated. Our first aim was to determine which model (i.e. partial least squares regression (PLSR), Cubist, random forest (RF), or support vector machine regression (SVMR)) produces the best prediction of topsoil exch. Ca, Mg, K and Na. The second aim was to evaluate if the best topsoil model can be used to predict subsurface (0.3–0.6 m) and subsoil (0.9–1.2 m) exch. cations. The third aim was to explore the effect of spiking on the prediction in subsurface and subsoil using the topsoil spectral library. The fourth aim was to see if combining all depths to build a profile spectral library improved prediction. Based on independent validation, PLSR was superior for topsoil exch. cations prediction, while Cubist outperformed PLSR in some cases when spiking was applied, and the profile spectral library was considered. Topsoil PLSR could be applied to predict exch. Ca and Mg in the subsurface and subsoil, while spiking improved prediction. Moreover, a profile spectral library achieved equivalent results with when topsoil samples coupled with spiking were considered. We, therefore, recommended to predict exch. Ca and Mg throughout the profile using topsoil spectral library coupled with spiking approach.

Role of Microalgae in the Recovery of Nutrients from Pig Manure

Animal production inevitably causes the emission of greenhouse gases and the generation of large amounts of slurry, both representing a serious environmental problem. Photosynthetic microorganisms such as microalgae and cyanobacteria have been proposed as alternative strategies to bioremediate agricultural waste while consuming carbon dioxide and producing valuable biomass. The current study assessed the potential of the microalga Scenedesmus sp. to remove nutrients from piggery wastewater (PWW) and the influence of the microalga on the microbial consortia. Maximum N-NH4+ consumption was 55.3 ± 3.7 mg·L−1·day−1 while P-PO43− removal rates were in the range 0.1–1.9 mg·L−1·day−1. N-NH4+ removal was partially caused by the action of nitrifying bacteria, which led to the production of N-NO3−. N-NO3− production values where lower when microalgae were more active. This work demonstrated that the photosynthetic activity of microalgae allows us to increase nutrient removal rates from PWW and to reduce the coliform bacterial load of the effluent, minimising both their environmental impact and health risks. Microalgae assimilated part of the N-NH4+ present in the media to produce biomass and did not to convert it into N-NO3− as in traditional processes.

Review on carbon dioxide fixation coupled with nutrients removal from wastewater by microalgae

The application of microalgae in carbon dioxide (CO2) fixation coupled with wastewater treatment has been regarded as a promising and cutting-edge technology in recent years, but it still faces some problems. The CO2 fixation capacity and nutrients removal capacity of microalgae should be considered simultaneously under various environmental conditions. Moreover, breeding microalgae using a photobioreactor is required and critical for CO2 fixation and wastewater treatment. In addition, the related influenced factors, mechanisms and kinetics of CO2 fixation and nutrients removal by microalgae remains complex and unclear. Thus, this work provides an updated review of the literature regarding the application of microalgae in the remediation of wastewaters from different sources coupled with CO2 fixation, discusses the main interactions between biological or environmental factors and how they can influence nutrient removal and CO2 fixation efficiencies, and further focuses on their mechanisms and kinetics. It is found that blue-green algae are most suitable to fix CO2 integrating treated wastewater, but more microalgal strains with excellent anti-fouling performance, tolerance to high concentrations of CO2 and NH3–N performance need to be screened. Additionally, wastewater and gas conditions during the cultivation process should be optimized in research and applications, and development of innovative photobioreactors with low cost is also required. Furthermore, modelling mainly focuses on estimating biomass yield, nutrient removal rates and CO2 fixation rates, while laboratory modelling results deviated from the natural modelling results. Finally, this paper also provides insight into what should be done in future work to support the development of CO2 fixation coupled with wastewater treatment by microalgae.

Root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus over the period of plant establishment in a constructed floating wetland.

Constructed floating wetlands have been employed worldwide to treat effluents and to ameliorate water quality of water resources. However, the period of macrophyte establishment into the hydroponic functioning has not been specifically addressed. This paper reports root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus in a floating structure without growth substrates over the period of 11 weeks of macrophyte establishment. The experiment was conducted in mesocosm with two replicas of each specie. Weekly batches were applied with three different concentrations of a synthetic effluent. Root growth was measured to evaluate the macrophyte adaptation. Physicochemical parameters were weekly monitored, and total nitrogen, nitrate, total phosphorus, and orthophosphate were quantified to assess nutrient removal. Both species have adapted to the floating structure, but T. domingensis presented superior root growth in relation to S. californicus. No significant differences were found during the application of first two synthetic solutions. As to solution 3, significant differences between input and output values were found to total phosphorus (F = 9.948, df = 1, p = 0.008), nitrate (F = 5.990, df = 1, p = 0.031), and total nitrogen (F = 40.212, df = 1, p < 0.0001). Removal efficiency of T. domingensis ranged from 4 to 31% for total nitrogen and from 8 to 15% for total phosphorus. S. californicus, on the other hand, varied its removal efficiency from - 6 to 5% and 2 to 12% for total nitrogen and total phosphorus, respectively. Time period of macrophyte establishment varied between species, and it was an important factor that contributed to the increase of nutrient removal rates and root growth.

Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS

Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.

Can luminescent solar concentrators increase microalgal growth on anaerobically digested food effluent?

Increasing microalgal biomass productivity and enhancing nutrient removal rates are critical when growing microalgae in wastewater. In most cases, the effluents such as anaerobically digested food effluent (ADFE) are very turbid. Using such effluents as a medium for an algal culture would leave the culture with high turbidity resulting in photo-limitation of the algal culture. Light-diffusing systems can be used to overcome the light limitation in microalgal cultures. In this study, red luminescent solar concentrators were used to shift the sunlight into the desired wavelength and deliver it into the depth of cultures of an outdoor microalgal consortium cultivated in ADFE in paddlewheel-driven raceway ponds. Biomass productivity and specific growth rate of cultures grown using red luminescent solar concentrators (LSCs) were 61% and 59% higher than those in control cultures. The nitrogen assimilation rate of biomass under red LSCs was 1.8-fold higher than that in the control. Further, the lipid content of the cultures under red LSCs (490 mg lipid g−1 biomass) was 30% higher than that of the control. The results of this study showed that using red LSCs can improve microalga growth on ADFE when paddlewheel raceway ponds are used.