Nutrient-rich Wastewater Research Articles

Lowering pH enables duckweed (Lemna minor L.) growth on toxic concentrations of high-nutrient agricultural wastewater

The use of duckweed species to remediate nutrient-rich wastewater has grown as a field of research and in industry; however, the need to dilute wastewater to the low ammoniacal-N concentrations tolerated by duckweed represents a barrier to commercially implementing these systems in agriculture. This study investigated the potential for acidifying anaerobically digested cattle slurry (digestate), shifting the NH4+:NH3 equilibrium towards the less toxic ionised form, thus allowing the growth of Lemna minor on less dilute wastewater. First, a study was conducted to identify the ammoniacal-N concentrations tolerated by L. minor and to confirm the positive effect of lower pH on growth in high nutrient solutions using modified Hutner's solutions at two pH levels (8.2 and 6.5). In Hutner's solution at a pH of 8.2, L. minor growth was highest at the lowest ammoniacal-N concentration of 10 mg L−1 and decreased with increasing concentrations. At a pH of 6.5, L. minor growth remained unaffected with increasing ammoniacal-N up to a concentration of 250 mg L−1. L. minor was then grown in digestate concentrations ranging from 5% (65 mg L−1 ammoniacal-N) to 30% (350 mg L−1 ammoniacal-N), based on its growth in Hutner's solutions. It was hypothesised, that growth would decrease as the digestate concentration increased at pH 8.2, and that acidifying digestate to pH 6.5 would alleviate this effect. On unamended digestate (pH 8.2), L. minor growth was prevented even in the most dilute treatment (5%); however, on acidified digestate (pH 6.5), growth rates remained positive and significantly higher than the unamended controls up to the 20% dilution (239.3 mg L−1 ammoniacal-N). Higher growth rates in the Hutner's solutions compared to digestate, particularly at pH 8.2 where no growth was recorded in digestate, suggest the presence of additional inhibitory factors in complex, high-nutrient wastewaters, and potentially sub-optimal concentrations of some of the nutrients provided in Hutner's solution. Nevertheless, correlation matrix analysis of digestate chemical properties highlighted the importance of acidification, with a strong negative correlation between pH and L. minor growth rate. For the first time, we demonstrate that by lowering pH, L. minor could be grown on dilutions of nutrient-rich agricultural wastewater that were otherwise toxic, and which make it feasible as a nutrient removal method. These findings could have important implications for implementing duckweed-based remediation systems in agriculture, increasing water- and land use efficiency, and thus, their commercial viability.

Effects of nutrient reduction and habitat heterogeneity on benthic macroinvertebrate assemblages in a large shallow eutrophic lake

The Taihu Lake ecosystem has been subjected to numerous anthropogenic stressors during the past decades, leading to substantial changes in nutrient dynamics and habitat quality. For instance, the northwestern lake bays receive large amounts of nutrient-rich wastewater and have frequently experienced algal blooms, while the eastern lake region is still dominated by submersed macrophytes. Such changes in environmental characteristics can greatly impact benthic macroinvertebrate communities. We used a 15-year monitoring data series collected by the Taihu Laboratory for Lake Ecosystem Research to examine the spatial and temporal variations of the benthic invertebrate fauna and evaluate its status and trends. We found that three major communities could be distinguished based on taxonomic group composition and abundance, and these corresponded well with three lake habitat types: algal-dominated, macrophyte-dominated, and open-lake zone. An analysis of temporal trends showed major changes in the macroinvertebrates during the study period, largely driven by a lake-wide and significant decline in the abundance of pollution-tolerant taxa. The spatial and temporal variations of macroinvertebrate communities were mainly explained by nutrients (e.g., total nitrogen and ammonium concentrations) and habitat factors (e.g., sediment substrates and macrophyte biomass) as indicated by Random Forests regression, but the major drivers of macroinvertebrate density differed among the three lake zones at the temporal scale. Moreover, our findings suggest that benthic invertebrates were more sensitive to the improvement of the lake's environmental conditions than the pelagic community was. This study provides insights into the responses of macroinvertebrates to ecological dynamics in lakes and highlights the importance of continued monitoring for tracking long-term changes.

Treatment of emerging contaminants in simulated wastewater via tandem photo-Fenton-like reaction and nutrient recovery

Nutrient rich wastewater containing emerging organic contaminants was used for struvite synthesis with a novel tandem process with a heterogeneous Fenton oxidation pretreatment.

Comprehensive insights into conversion of microalgae to feed, food, and biofuels: Current status and key challenges towards implementation of sustainable biorefineries

Microalgae have been promoted as important feedstocks for producing biofuels and bioproducts. However, their production on a large scale would require a large amount of water and nutrients. Considering the importance of food security and the high economic value of microalgal biomass, food and feed applications should be prioritized if microalgae are grown using conventional water resources. Nevertheless, microalgae can also be grown in nutrient-rich wastewater streams while producing valuable biomass and treating harmful effluents. Because of health issues, food and feed applications of microalgal biomass grown using waste resources are not allowed; hence, it can be used as a feedstock for biofuel production. In line with that, this review first briefly discusses the applications of microalgae in food, feed, and wastewater treatment and then summarizes the efforts put into utilizing microalgal biomass to produce biofuels through different pathways. These technologies, including thermochemical (200–1300 °C), biochemical (25–55 °C), and chemical (25–200 °C) conversion methods, are critically discussed. The pros and cons of using different microalgal conversion technologies are outlined to identify possible future directions for the field. Different microalgal biomass harvesting methods are also reviewed, and the process conditions are summarized. Parameters affecting technology selection, such as energy costs, reaction time, and technological sophistication, are also explored and presented. In general, microalgal biofuels still face many challenges in replacing traditional fossil fuels. Future work should focus on maximizing the yield and quality of microalgal biofuels while enhancing their economic viability.

The potential role of sediments in nutrients (N, P) cycle in Marchica lagoon (Mediterranean Sea, Morocco)

The aim of this study is to present the distribution of nutrients in water and sediment of Marchica lagoon, a post-restorated lagoon located in Mediterranean Sea (NE Morocco), to estimate the impact of bottom sediments on the water quality of this lagoon, and to identify the areas more affected by eutrophication risk. Nutrient concentrations in the water column and sediments were determined in thirteen samples taken from different station of the lagoon in October 2019. Nutrient concentrations in sediment were found higher than those in surface water; very high levels of nitrogenous elements showed in all sediments samples and mainly nitrogenous components (averages of 43.58 mg of N-NH4; 0.827 mg of N-NO3; 0.054 mg of N-NO2 and 773 mg of TN per kg of dry sediment) and high levels of phosphorus with average of 620 mg P/kg of dry sediment. A strong positive correlation showed between sediment and water parameters in 0.01 and 0.05 levels. High concentrations were recorded near the nutrient-rich wastewater treatment plant effluent discharges, watershed and groundwater input. The lowest concentrations are near the new pass, this is due to the low continental inputs and the renewal of the lagoon waters by the Mediterranean Sea. Generally, the distribution of nutrient levels is influenced by continental inputs, hydrodynamics, and organic matter content in the sediment. These sediments are considered as a reservoir of nutrient pollutants, which will influence water quality by releasing sedimentary materials in the water.

Potential of microalgae cultivation using nutrient-rich wastewater and harvesting performance by biocoagulants/bioflocculants: Mechanism, multi-conversion of biomass into valuable products, and future challenges

Microalgae have been identified as one of the new feedstocks for renewable energy production . The conversion of microalgae into various valuable products has also been increasing in the last decade. Microalgae harvesting, one of the most important stages in microalgae production, has been studied and reviewed by many researchers. However, most harvesting methods still utilize chemicals during the process, which make harvested biomass not directly ready for food/feed production and pharmaceutical-related processes. Biocoagulants/bioflocculants are emerging compounds that can be used during the harvesting of microalgae because their existence does not introduce toxicity in the harvested biomass. Considering its potential to produce ready-to-use biomass, biocoagulants/bioflocculants have a bright future in microalgal biomass production processes. This review article highlights simultaneous wastewater treatment and microalgal biomass production as an emerging method in accommodating a circular economy paradigm. This paper juxtaposes the utilization of chemical-based coagulants/flocculants and biocoagulants/bioflocculants in harvesting microalgae. Biodegradability , effectiveness, harvested biomass characteristics, and potential of medium reuse are emphasized in the discussion. The agglomeration mechanisms of microalgae during harvesting, recent advances in the microalgal biomass conversions, and future challenges related to the utilization of biocoagulants/bioflocculants are also described in detail. Microalgae harvesting by using biocoagulants/bioflocculants is a feasible and promising environmentally friendly technology for microalgal biomass production. • Performances of microalgae harvesting using biocoagulants/bioflocculants are discussed. • Cultivation of microalgae using wastewater is discussed. • Mechanisms of microalgae harvesting are elaborated. • Conversion of microalgae biomass into valuable products are highlighted. • Future challenges on algae harvesting using biocoagulants/bioflocculants are discussed.

Performance of Chlorella sp. and Multicultural Bacteria in Removing Pollutants from Nutrient-Rich Wastewater

The most common method of treating palm oil mill effluent (POME) is by using various types of bacteria communities. However, the utilization of microalgae in consuming the high nutrient content in wastewater offer additional benefit, particularly for CO2 sequestration. In this study, we proposed to evaluate the performance of multicultural bacteria obtained from municipal wastewater and Chlorella sp. for batch treatment of POME at different COD concentrations (ranges between 600 to 1,300 mg/L), microalgae species (C. vulgaris and C. pyrenoidosa) and speed of agitation (0 and 150 rpm). The results showed that between the bacteria and microalgae that are involved in POME treatment, microalgae give high removal of colour (93%) and ammoniacal nitrogen (95%). As for the COD and phosphate removal, both microorganisms show comparable performances. It was observed that C. pyrenoidosa was able to remove more colour compared to C. vulgaris where higher lipid yield production was obtained (47.6%). However, there is no significant impact of agitation on pollutant removal. This study also reveals that co-cultivation of different microalgae species does not affect the efficiency of the system. This study provides an important insight into developing an efficient and environmentally friendly method to treat wastewater by incorporating green technology in the treatment system

Wastewater substrate disinfection for cyanobacteria cultivation as tertiary treatment.

Cultivation of microalgae or/and cyanobacteria in nutrient-rich wastewaters offers an opportunity for enhancing sustainability of tertiary wastewater treatment processes via resources/energy recovery/production, mitigation of emitted GHGs and provision of added value products. However, maintaining a monoculture in wastewater-media constitutes a significant challenge to be addressed. In this regard, the present work assesses the efficiency of the low-cost wastewater substrate disinfection techniques of filtration, use of NaClO, H2O2 or Fe(VI), as a preliminary treatment stage upstream a cyanobacteria cultivation photobioreactor. The growth rate of cyanobacterium Synechococcus elongatus PCC 7942, and nitrate and phosphate removal rates, were experimentally assessed in cultivation setups with biologically treated dairy wastewater that had been subjected to a single or a synergetic couple of disinfection techniques. The results showed that filter thickness has a greater effect on disinfection efficiency than filter pore size. Furthermore, the disinfection efficiency of Fe(VI), which was produced on-site by electrosynthesis via a Fe0/Fe0 cell, was greater than that of NaClO and H2O2. Filtration at ≤ 1.2-μm pore size coupled with chemical disinfection led to unhindered Synechococcus elongatus PCC 7942 growth and efficient nitrate and phosphate removal rates, at dosages, in terms of Concentreation-Time (CT) product,of CT ≥ 270mgmin L-1 for NaClO and CT ≥ 157mgmin L-1 for Fe(VI). The coagulation action of Fe(III) species that result from Fe(VI) reduction and the oxidation action of Fe(VI) can assist in turbidity, organic compounds and phosphorous removal from wastewater media. Moreover, the residual iron species can assist in Synechococcus elongatus PCC 7942 harvesting and may enhance photosynthesis rate by increasing light transfer efficiency. Thus, a filtration configuration coupled with chemical disinfection, preferably using ferrates, downstream of sedimentation tank of a secondary biological wastewater treatment stage is proposed as a necessary, efficient and low-cost disinfection technique for full-scale scale implementation of cyanobacteria cultivation as tertiary wastewater processes.

Process optimization of struvite recovered from slaughterhouse wastewater and its fertilizing efficacy in amendment of biofertilizer

The intensive discharge of slaughterhouse waste into water bodies increases Nitrogen (N), Phosphorus (P) in the wastewater and leads to various environmental problems. On the other hand, the increasing treatment effort after the extraction of these valuable nutrients in the commercial fertilizer reduces the dependence on scarce phosphate resources. The viable solution is to recover N, P as struvite (magnesium ammonium phosphate) from nutrient rich waste water as a small scale treatment unit application. The main parameters that have a significant impact on the process, including pH, Mg: P ratio, and precipitation time, were investigated from slaughterhouse wastewater using a central composite design and the experimental data's were statistically analysed. The results indicated that pH and Mg/P ratio level had a significant impact and thus 85% struvite precipitation efficiency was achieved at 9.6 pH and 1.5 dose mol ratio (mol Mg per mol P), in an inexpensive, stirred tank batch reactor with a retention time of 70 min. The fertilization efficiency was tested on the growth of Solanum melongena L with the obtained struvite and the integration of struvite with the Azospirullum rhizobium and Bacillus megaterium. Treatment of struvite, struvite with Azospirillum rhizobium and Bacillus megaterium increased growth parameters by 10%, 20%, and 25%, respectively, over control. The assessment of growth factors showed the most amazing number of fruits, shoots, and root length in a standard ratio of 60:40 of struvite to bio-inoculants compared to sole struvite fertilizer. Findings of this study would be beneficial to determine the feasibility of slaughterhouse waste as a phosphorus source for struvite recovery.

High-Efficiency Production of Auricularia polytricha Polysaccharides Through Yellow Slurry Water Fermentation and Its Structure and Antioxidant Properties.

Yellow slurry water is a kind of nutrient-rich wastewater of tofu. Firstly, the medium of yellow slurry was optimized. Then, APP40, APP60, and APP80 were obtained by sedimentation with different concentration of ethanol (40, 60, and 80%). The physicochemical properties and primary structures of the three polysaccharides were studied by high performance anion exchange chromatography (HPAEC), high performance gel filtration chromatography (HPGFC), scanning electron microscope (SEM), atomic force microscope (AFM), and Fourier transform infrared (FT-IR) spectrometer. Finally, the effects of three polysaccharides on antioxidation activity were studied. According to the experimental optimization the results, the biomass and the production of Auricularia polytricha Polysaccharides (APPS) reached the peak, and they were 13.5 ± .655 and 9.42 ± .253 g/L (p < .05). The SEM and the AFM showed that the height of APP80 gradually increased from 31.1 to 46.7 nm and from APP40 to APP80. The particle size of APP80 increased, the pores decrease or even disappear, and the molecules begin to aggregate. The FT-IR spectrum analysis showed that the three polysaccharides possessed key functional groups. The carbohydrate content of APP40, APP60, and APP80 was 20.2, 34.25, and 31.73%. The molecular weights of APP40, APP60, and APP80 are 9.462 × 104, 8.742 × 104, and 8.091 × 104 Da, respectively. The three polysaccharides were composed of rhamnose, galactose, glucose, mannose, and xylose but with different molar ratio. APP80 showed strong reducing ability and scavenging activity of 2,2–diphenyl–1–picrylhydrazyl (DPPH) and hydroxyl radicals through antioxidant activities evaluated in vitro. This study introduces a way for the effective use of yellow slurry water.

Volume, biomass, carbon sequestration and potential of desert lands’ afforestation irrigated by wastewater on examples of three species

A study was conducted on three species (Khaya senegalensis, Corymbia citriodora and Casuarina equisetifolia) planted in desert lands of Egypt and irrigated with basic treated municipal wastewater. Every single tree is permanently drip irrigated and at the same time fertilised by the nutrient-rich wastewater. Trees of different classes of the diameter at breast height (eight for each species) were felled to determine the form factor and stem volume, as well as the biomass and carbon sequestration of stem, crown and root of the individual trees. In addition, a scenario for the development of un-thinned stands from ages 5 to 35 years was constructed. The age of the sample trees at felling was: 128, 66 and 82 months for K. senegalensis, C. citriodora and C. equisetifolia, respectively. The vigorous sampled trees had a stem volume of 0.289, 0.162 and 0.229 m3 and an aboveground and belowground biomass of 451, 161 and 264 kg for K. senegalensis, C. citriodora and C. equisetifolia, respectively. Results of the scenario showed an unexpectedly high growth rate of afforestation in desert lands using municipal wastewater. At the age of 25, the stem volume for all three species exceeds 398 m3/ha. At the same age of 25 years, K. senegalensis, C. citriodora and C. equisetifolia sequester 1131, 1068 and 860 CO2 t/ha, respectively. Afforestation in desert areas presents a unique situation in forestry, as growth is stimulated by sufficient sunlight, water and nutrients. Competition for water and nutrients is strongly diminished. Self-thinning of stands under such conditions is expected to be much slower than in rain-fed plantation forests. On the other hand, tree maturity span is curtailed. This opens new possibilities for different forest management and practices towards resilient forest-based mitigation of climate change. For its unexpected role as an effective mitigation measure, afforestation in desert lands should be encouraged and further research conducted.

Engineering Calcium-bearing Mineral/Hydrogel Composites for Effective Phosphate Recovery.

Effectively recovering phosphate from wastewater streams and reutilizing it as a nutrient will critically support sustainability. Here, to capture aqueous phosphate, we developed novel mineral-hydrogel composites composed of calcium alginate, calcium phosphate (CaP), and calcium silicate (CSH) (CaP + CSH/Ca-Alg). The CaP + CSH/Ca-Alg composites were synthesized by dripping a sodium alginate (Na-Alg) solution with ionic precursors into a calcium chloride bath. To change the mineral seed's properties, we varied the calcium bath concentrations and the ionic precursor (sodium dibasic phosphate (NaH2PO4) and/or sodium silicate (Na2SiO3)) amounts and their ratios. The added CSH in the mineral-hydrogel composites resulted in the release of calcium and silicate ions in phosphate-rich solutions, increasing the saturation ratio with respect to calcium phosphate within the mineral-hydrogel composites. The CSH addition to the mineral-hydrogel composites doubled the phosphate removal rate while requiring lesser initial amounts of Ca and P materials for synthesis. By incorporating both CSH and CaP mineral seeds in composites, we achieved a final concentration of 0.25 mg-P/L from an initial 6.20 mg-P/L. Moreover, the mineral-hydrogel composites can remove phosphate even under CaP undersaturated conditions. This suggests their potential to be a widely applicable and environmentally-sustainable treatment and recovery method for nutrient-rich wastewater.

Optimum operational conditions for mixotrophic microalgae growth and nutrient recovery

Microalgae have been presented as microorganisms with great potential to recover nutrient from wastewater. Mixotrophic cultivation of microalgae in nutrient rich wastewater can help eliminating the deficiencies of both phototrophic and heterotrophic growth by allowing the independent optimisation of respiration and photosynthesis processes. Nutrient control and uptake by mixotrophic microalgae can be achieved either in a single or two-stage process using sequential reactors in a continuous flow system. Therefore, this work aims at studying mixotrophic microalgae growth in a two-stage biological process under continuous flow conditions with biomass recycle to recover nutrients from wastewater, considering the effects of different operational conditions (hydraulic retention time (HRT), cell retention time (CRT) and different nitrogen sources). The optimum operational conditions for algal nutrient uptake were identified to be 48 h HRT and 14 d CRT, using a mix of nitrogen sources (Ammonium-N to Nitrate-N ratio of 1:1) with 40.0% and 93.2% of phosphorus of nitrogen recovery in algal biomass, respectively.

Response of simultaneous nitrification-denitrification to DO increments in continuously aerated biofilm reactors for aquaculture wastewater treatment

Abstract Intensive aquaculture usually produces large volumes of nutrient-rich wastewater, which is essential to treat to avoid eutrophication. This study aimed to evaluate the performance of five continuously aerated biofilm reactors treating simulated high-strength aquaculture wastewater under different dissolved oxygen (DO) levels, and the effects of DO increments on simultaneous nitrification-denitrification (SND). Continuous aeration was beneficial to complete nitrification. Total inorganic nitrogen (TIN), principally ammonium, was mainly removed by SND. The SND rate response to different DO levels was fitted well by the power function of y = 54.81 + 371.58/(1 − 0.16*x)^(−1/0.24) (R2 = 0.897, P = 0.000). When the TIN was removed completely, the optimal SND rate was defined and corresponded to a value of 121.8%. Accordingly, the optimal DO concentration was calculated as 2.10 mg/L, close to the actual level of 1.83 mg/L, at which the highest proportional removals of total nitrogen (58.0%) and TIN (57.3%) were obtained. Phosphorus was also removed by denitrifying polyphosphate-accumulating organisms.

Nutrient Enrichment of Wastewater Generated During Hydraulic Fracturing with Animal Wastewater to Enhance Microalgae Growth

Hydraulic fracturing technology widely used for recovery of oil and gas from tight shale formations generate millions of gallons of wastewater. This study examined viability of algal remediation of the hydraulic fracturing wastewater (HFWW). Our previous studies have shown that although Oklahoma native algae strains can grow in HFWW, cell growth was constrained by the low nutrient concentrations in HFWW. Hence, the goal of this study was to examine the effect of nutrient supplementation of HFWW with another nutrient rich wastewater on microalgae growth. An Oklahoma, USA, native algae strain, Picochlorum oklahomensis, was selected for the study because of its high biomass productivity in wastewater. This study demonstrated that P. oklahomensis can grow in HFWW. Supplementation of the HFWW with animal wastewater enhanced biomass productivity and lipid content of the biomass. Chemical compositions of the wastewater before and after algae growth were significantly different indicating substantial amount of contaminant removal.

Improving the Fertigation of Soilless Urban Vertical Agriculture Through the Combination of Struvite and Rhizobia Inoculation in Phaseolus vulgaris.

Soilless crop production is a viable way to promote vertical agriculture in urban areas, but it relies extensively on the use of mineral fertilizer. Thus, the benefits of fresher, local food and avoiding the transportation and packaging associated with food import could be counteracted by an increase in nutrient-rich wastewater, which could contribute to freshwater and marine eutrophication. The present study aimed to explore the use of mineral fertilizer substitutes in soilless agriculture. Phaseolus vulgaris (common bean) was fertilized with a combination of slow-releasing fertilizer struvite (a source of N, P, and Mg), which is a byproduct of wastewater treatment plants, and inoculation with Rhizobium (a N2-fixing soil bacteria). The experiment included three bean-production lines: (A) 2 g/plant of struvite and rhizobial inoculation; (B) 5 g/plant of struvite and rhizobial inoculation, both irrigated with a Mg-, P-, and N-free nutrient solution; and (C) a control treatment that consisted of irrigation with a full nutrient solution and no inoculation. Plant growth, development, yields, and nutrient contents were determined at 35, 62, and 84 days after transplanting as well as biological N2 fixation, which was determined using the 15N natural abundance method. Treatments A and B resulted in lower total yields per plant than the control C treatment (e.g., 59.35 ± 26.4 g plant–1 for A, 74.2 ± 23.0 g plant–1 for B, and 147.71 ± 45.3 g plant–1 for C). For A and B, the nodulation and N2 fixation capacities appeared to increase with the amount of initially available struvite, but, over time, deficient levels of Mg were reached as well as nearly deficient levels of P, which could explain the lower yields. Nevertheless, we conclude that the combination of struvite and N2-fixing bacteria covered the N needs of plants throughout the growth cycle. However, further studies are needed to determine the optimal struvite quantities for vertical agriculture systems that can meet the P and Mg requirements throughout the lifetime of the plants.

Co-application of biogas slurry and hydrothermal carbonization aqueous phase substitutes urea as the nitrogen fertilizer and mitigates ammonia volatilization from paddy soil

Biogas slurry (BS) and bio-waste hydrothermal carbonization aqueous phase (HP) are nutrient-rich wastewater. To prevent environment contamination, transforming BS and HP into synthetic fertilizers in the agricultural field can potentially realize resource utilization. We hypothesized that acidic HP could neutralize alkaline BS, adjusting floodwater pH from 6.88 to 8.00 and mitigating ammonia (NH3) volatilization from the paddy soil. In this soil column study, the mixture of BS and HP was applied to paddy soil to substitute 50%, 75%, and 100% to urea. With a low (L) or high (H) ratio of HP, treatments were labeled as BCL50, BCL75, BCL100, BCH50, BCH75, and BCH100. Results showed that microbial byproduct- and fulvic acid-like substance were the main components in BS and HP using 3D-EEM analysis, respectively. Co-application of BS and HP mitigated the NH3 volatilization by 4.2%–65.5% compared with CKU. BCL100 and BCH100 treatments significantly (P < 0.05) mitigated NH3 volatilization by 65.5% and 56.8%, which also significantly (P < 0.05) mitigated the yield-scale NH3 volatilization by 49.6% and 42.3%, compared with CKU. The low NH4+-N concentration and pH value in floodwater were the main reason explained the NH3 mitigation. Therefore, this study demonstrated that BS and HP co-application can substitute the urea as a valuable N fertilizer in a rational rate and meanwhile mitigate the NH3 volatilization. This study will provide new ideas for the utilization of BS and HP resources in the context of ammonia mitigation.

Engineering principles and process designs for phosphorus recovery as struvite: A comprehensive review

The rising population relies heavily on expensive phosphate (P) fertilizers for its agricultural productivity that qualms the national food security. Globally, there is a growing concern for the profound reliance on finite phosphorite reservoirs for commercial phosphate fertilizers’ qualitative and quantitative production. On the contrary, uncontrolled discharging of nutrient-rich wastewaters into natural streams, affecting the aquatic ecosystem. These critical situations have caused a scientific threat that has forced the researchers to explore other opportunities for the conservation of nutrient resources, recovery, and recycling. This review examines the nutrient recovery paradigms for struvite production by curtailing the nutrient gap between wastewater treatment and agricultural productivity. It comprehends the fundamental chemistry, thermodynamics, and factors influencing the struvite production process with its detailed mechanisms. Further, it deliberates the possible struvite engineering strategies, including process designs to enhance P recovery at the lab, pilot, and commercial scale. Also, it emphasizes the applications of nutrient-loaded struvite as a slow-release fertilizer and the challenges associated with economic feasibility and scaling up of the process in recent decades.

The determination of fertiliser quality of the formed struvite from a WWTP.

Struvite from nutrient-rich wastewaters has been identified as a potential substitute for commercial mineral fertilisers, with the added benefit of reducing threats to global food security by prolonging phosphate rock reserves. A fertilisation test using grass (Brachiaria brizantha Marandú) and a sand column leaching test was conducted to determine the agronomic effectiveness of struvite precipitates produced from the supernatant of dewatered sewage sludge (centrate) from a municipal Wastewater Treatment Plant (WWTP). The performance of this struvite as a fertiliser was compared with biosolids and commercial fertilisers (Urea and Triple15). The results show that the concentration of heavy metals in struvite was lower than in biosolids and below the limits of Colombia and European fertiliser regulations. Struvite increased the uptake of N and P in grass, resulting in crop yields similar to other treatments tested. Struvite use as an effective slow-release fertiliser is highly dependent on the size of crystal particles, particularly in achieving low P losses, but resulted in high N loss in the sand columns tested; N loses from struvite were higher than in the commercial fertilisers due to the struvite small particle size. Therefore, struvite represents a suitable opportunity to recover and recycle nutrients from municipal sewage sludge, facilitating the effective reuse of P and N in agriculture and uptake by plants.

Recent technologies for nutrient removal and recovery from wastewaters: A review

Water scarcity and its pollution has become a concern in recent times. The disposal of nutrient-rich (nitrogen and phosphorous) wastewater is also one of the main cause of water pollution through eutrophication, reduced dissolved oxygen that poses threat to aquatic ecosystems. As a result, nutrient removal has become a mandate apart from the removal of organics. However, the removal of nutrients from sewage is a challenging task. Conversely, conventional biological treatment processes provide little relief in nutrient removal. The treated effluents from conventional biological processes do not achieve the stringent nutrient removal disposal standard limits and become primary cause of pollution in the receiving water bodies. This has stressed upon the need for eco-friendly, low-energy and cost-efficient nutrient removal treatment technologies. Various biological treatment combinations or variants are in use for the efficient removal of nutrients. The biological processes in itself or in combination with chemical processes are preferred over technologies based solely on physico-chemical processes for its treatment performance at lower cost. This review summarizes the existing treatment processes and their possible up-gradation with the aim to accomplish the marked effluent standards for the nutrients. The concept of conventional systems and advanced systems for nutrients (nitrogen and phosphorous) removal which are already developed or under development are deeply discussed. Further, the challenges of each treatment systems are abridged. Finally, the possible suggestions for the modification/retrofitting of existing treatment systems for achieving stringent disposal standards are pointed out.