Strategies for livestock wastewater treatment and optimised nutrient recovery using microalgal-based technologies.

Global sustainable development faces several challenges in addressing the needs of a growing population. Regarding food industries, the heightening pressure to meet these needs has resulted in increased waste generation. Thus, recognising these wastes as valuable resources is crucial to integrating sustainable models into current production systems. For instance, the current 24 billion tons of nutrient-rich livestock wastewater (LW) generated yearly could be recovered and valorised via biological uptake through microalgal biomass. Microalgae-based livestock wastewater treatment (MbLWT) has emerged as an effective technology for nutrient recovery, specifically targeting carbon, nitrogen, and phosphorus. However, the viability and efficacy of these systems rely on the characteristics of LW, including organic matter and ammonium concentration, content of suspended solids, and microbial load. Thus, this systematic literature review aims to provide guidance towards implementing an integral MbLWT system for nutrient control and recovery, discussing several pre-treatments used in literature to overcome the challenges regarding LW as a suitable media for microalgae cultivation.

Effect of macronutrients (carbon, nitrogen, and phosphorus) on the growth of Chlamydomonas reinhardtii and nutrient recovery under different trophic conditions.

More stringent discharge standards have led to the development of an alternative nutrient recovery system from wastewater. Microalgae cultivation in wastewater treatment works has presented considerable promise from the perspective of sustainable resource management. Growth kinetics models are useful tools to optimize nutrient recovery from wastewater by algal uptake. Therefore, this research aims to identify the growth kinetics of Chlamydomonas reinhardtii under both heterotrophic and phototrophic conditions with different nutrient concentrations that typify those found in wastewater treatment works. In addition, the effects of macronutrients (C, N, and P) on heterotrophic and phototrophic microalgae growth and nutrient recovery were studied. Greater specific growth rates were achieved under heterotrophic conditions than in phototrophic cultivation. The maximum specific growth rates and nutrient recovery efficiencies were achieved at 5 mg P L-1 under both heterotrophic and phototrophic growth conditions. Nitrate was the preferred form of nitrogen source under heterotrophic conditions, while nitrogen sources did not present any significant influences in the phototrophic cultivation. Specific growth rates reported for both heterotrophic and phototrophic microalgae at lower carbon concentrations (3.10 d-1 and 0.46 d-1, sequentially) were higher than those at higher carbon concentrations (1.95 d-1 and 0.22 d-1, respectively). C. reinhardtii presented an extreme capacity to adapt and grow at all experimental conditions tested in heterotrophic and phototrophic cultivations.

Overexpression of PSR1 in Chlamydomonas reinhardtii induces luxury phosphorus uptake.

Remediation using micro-algae offers an attractive solution to environmental phosphate (PO4 3-) pollution. However, for maximum efficiency, pre-conditioning of algae to induce 'luxury phosphorus (P) uptake' is needed. To replicate this process, we targeted the global regulator PSR1 (Myb transcription factor: Phosphate Starvation Response 1) for over-expression in algae. Manipulating a single gene (PSR1) drove uptake of both PO4 3- and a Mg2+ counter-ion leading to increased PolyP granule size, raising P levels 4-fold to 8% dry cell weight, and accelerated removal of PO4 3- from the medium. Examination of the gene expression profile showed that the P-starvation response was mimicked under P-replete conditions, switching on luxury uptake. Hyper-accumulation of P depended on a feed-forward mechanism, where a small set of 'Class I' P-transporter genes were activated despite abundant external PO4 3- levels. The transporters drove a reduction in external PO4 3- levels, permitting more genes to be expressed (Class II), leading to more P-uptake. Our data pointed toward a PSR1-independent mechanism for detection of external PO4 3- which suppressed Class II genes. This model provided a plausible mechanism for P-overplus where prior P-starvation elevates PSR1 and on P-resupply causes luxury P-uptake. This is because the Class I genes, which include P-transporter genes, are not suppressed by the excess PO4 3-. Taken together, these discoveries facilitate a bio-circular approach of recycling nutrients from wastewater back to agriculture.

Enhanced in-situ biomethanation of food waste by sequential inoculum acclimation: Energy efficiency and carbon savings analysis.

The increasing rate of food waste (FW) generation globally, makes it an attractive resource for renewable energy through anaerobic digestion (AD). The biogas recovered from AD can be upgraded by the methanation of internally produced carbon dioxide, CO2 with externally sourced hydrogen gas, H2 (biomethanation). In this work, H2 was added to AD reactors processing FW in three successive phases, with digestate from preceding phases recycled in succession with the addition of fresh inoculum to enhance acclimation. The concentration of H2 was increased for succeeding phases: 5%, 10% and 15% of the reactor headspace in Phase 1 (EH1), Phase 2 (EH2) and Phase 3 (EH3), respectively. The H2 utilisation rate and biomethane yields increased as acclimation progressed from EH1 through EH3. Biomethane yield from the controls: EH1_Control, EH2_Control and EH3_Control were 417.6, 435.4 and 453.3 NmL-CH4/gVSadded accounting for 64.8, 73.9 and 77.8% of the biogas respectively. And the biomethane yield from the test reactors EH1_Test, EH2_Test and EH3_Test were 468.3, 483.6, and 499.0 NmL-CH4/gVSadded, accounting for 77.2, 78.1 and 81.0% of the biogas respectively. A progressive in-situ biomethanation could lead to biomethane production that meets higher fuel standards for gas-to-grid (GtG) injections and vehicle fuel - i.e. >95% CH4. This would increase the energy yield and carbon savings compared to conventional biogas upgrade methods. For example, biogas upgrade for GtG by in-situ biomethanation could yield 7.3 MWh/tFW energy and 1343 kg-CO2e carbon savings, which is better than physicochemical upgrade options (i.e., 4.6-4.8 MWh/tFW energy yield and 846-883 kg-CO2e carbon savings).

Uncoupling growth from phosphorus uptake in Lemna: Implications for use of duckweed in wastewater remediation and P recovery in temperate climates.

Phosphorus (P) is an essential nutrient for crop growth and the second most limiting after N. Current supplies rely on P-rich rocks that are unevenly distributed globally and exploited unsustainably, leading to concerns about future availability and therefore food security. Duckweeds (Lemnaceae) are aquatic macrophytes used in wastewater remediation with the potential for nutrient recycling as feed or fertilizer. The use of duckweeds in this way is confined to tropical regions as it has previously been assumed that growth in the colder seasons of the temperate regions would be insufficient. In this study, the combined effects of cool temperatures and short photoperiods on growth and P uptake and accumulation in Lemna were investigated under controlled laboratory conditions. Growth and P accumulation in Lemna can be uncoupled, with significant P removal from the medium and accumulation within the plants occurring even at 8°C and 6-hr photoperiods. Direct measurement of radiolabeled phosphate uptake confirmed that while transport is strongly temperature dependent, uptake can still be measured at 5°C. Prior phosphate starvation of the duckweed and use of nitrate as the nitrogen (N) source also greatly increased the rate of P removal and in-cell accumulation. These results form the basis for further examination of the feasibility of duckweed-based systems for wastewater treatment and P recapture in temperate climates, particularly in small, rural treatment works.

A Simple and Non-destructive Method for Chlorophyll Quantification of Chlamydomonas Cultures Using Digital Image Analysis.

Growing interest in the use of microalgae as a sustainable feedstock to support a green, circular, bio-economy has led to intensive research and development initiatives aimed at increasing algal biomass production covering a wide range of scales. At the heart of this lies a common need for rapid and accurate methods to measure algal biomass concentrations. Surrogate analytical techniques based on chlorophyll content use solvent extraction methods for chlorophyll quantification, but these methods are destructive, time consuming and require careful disposal of the resultant solvent waste. Alternative non-destructive methods based on chlorophyll fluorescence require expensive equipment and are less suitable for multiple sampling of small cultures which need to be maintained under axenic growth conditions. A simple, inexpensive and non-destructive method to estimate chlorophyll concentration of microalgal cultures in situ from digital photographs using the RGB color model is presented. Green pixel intensity and chlorophyll a, b and total chlorophyll concentration, measured by conventional means, follow a strong linear relationship (R 2 = 0.985-0.988). In addition, the resulting standard curve was robust enough to accurately estimate chlorophyll concentration despite changes in sample volume, pH and low concentrations of bacterial contamination. In contrast, use of the same standard curve during nitrogen deprivation (causing the accumulation of neutral lipids) or in the presence of high quantities of bacterial contamination led to significant errors in chlorophyll estimation. The low requirement for equipment (i.e., a simple digital camera, available on smartphones) and widely available standard software for measuring pixel intensity make this method suitable for both laboratory and field-based work, particularly in situations where sample, qualified personnel and/or equipment is limited. By following the methods described here it should be possible to produce a standard curve for chlorophyll analysis in a wide range of testing conditions including different microalga cultures, culture vessel and photographic set up in any particular laboratory.

Fixing the Broken Phosphorus Cycle: Wastewater Remediation by Microalgal Polyphosphates.

Phosphorus (P), in the form of phosphate derived from either inorganic (Pi) or organic (Po) forms is an essential macronutrient for all life. P undergoes a biogeochemical cycle within the environment, but anthropogenic redistribution through inefficient agricultural practice and inadequate nutrient recovery at wastewater treatment works have resulted in a sustained transfer of P from rock deposits to land and aquatic environments. Our present and near future supply of P is primarily mined from rock P reserves in a limited number of geographical regions. To help ensure that this resource is adequate for humanity's food security, an energy-efficient means of recovering P from waste and recycling it for agriculture is required. This will also help to address excess discharge to water bodies and the resulting eutrophication. Microalgae possess the advantage of polymeric inorganic polyphosphate (PolyP) storage which can potentially operate simultaneously with remediation of waste nitrogen and phosphorus streams and flue gases (CO2, SOx, and NOx). Having high productivity in photoautotrophic, mixotrophic or heterotrophic growth modes, they can be harnessed in wastewater remediation strategies for biofuel production either directly (biodiesel) or in conjunction with anaerobic digestion (biogas) or dark fermentation (biohydrogen). Regulation of algal P uptake, storage, and mobilization is intertwined with the cellular status of other macronutrients (e.g., nitrogen and sulphur) in addition to the manufacture of other storage products (e.g., carbohydrate and lipids) or macromolecules (e.g., cell wall). A greater understanding of controlling factors in this complex interaction is required to facilitate and improve P control, recovery, and reuse from waste streams. The best understood algal genetic model is Chlamydomonas reinhardtii in terms of utility and shared resources. It also displays mixotrophic growth and advantageously, species of this genus are often found growing in wastewater treatment plants. In this review, we focus primarily on the molecular and genetic aspects of PolyP production or turnover and place this knowledge in the context of wastewater remediation and highlight developments and challenges in this field.

Valorisation of macroalgae via the integration of hydrothermal carbonisation and anaerobic digestion.

This study investigates the integration of hydrothermal carbonisation (HTC) with anaerobic digestion (AD) as a valorisation route for two macroalgae species; S. latissima (SL) and F. serratus (FS). HTC reactions were conducted at temperatures of 150 °C, 200 °C and 250 °C, with resulting hydrochars, process waters and hydrothermal slurries assessed for biomethane potential yields. Un-treated SL generated similar biomethane levels compared to all SL slurries. Whereas all FS slurries improved biomethane yields compared to un-treated FS. Hydrochars represent a greater energy carrier if used as a solid fuel, rather than a feedstock for anaerobic digestion. Integrating HTC and AD, through hydrochar combustion and process water digestion has a greater energetic output than anaerobic digestion of the un-treated macroalgae. Treatment at 150 °C, with separate utilisation of products, can improve the energetic output of S. latissima and F. serratus by 47% and 172% respectively, compared to digestion of the un-treated macroalgae.

Five pillars for stakeholder analyses in sustainability transformations: The global case of phosphorus.

Phosphorus is a critical agricultural nutrient and a major pollutant in waterbodies due to inefficient use. In the form of rock phosphate it is a finite global commodity vulnerable to price shocks and sourcing challenges. Transforming toward sustainable phosphorus management involves local to global stakeholders. Conventional readings of stakeholders may not reflect system complexity leaving it difficult to see stakeholder roles in transformations. We attempt to remedy this issue with a novel stakeholder analysis method based on five qualitative pillars: stakeholder agency, system roles, power and influence, alignment to the problem, and transformational potential. We argue that our approach suits case studies of individual stakeholders, stakeholder groups, and organisations with relationships to sustainability challenges.

Preparation of functionalized magnetic nanoparticles conjugated with feroxamine and their evaluation for pathogen detection.

This work reports the preparation of a conjugate between amino-functionalized silica magnetite and the siderophore feroxamine. The morphology and properties of the conjugate and intermediate magnetic nanoparticles (MNPs) were examined by powder X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), magnetization studies, zeta potential measurements, Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) mapping. Furthermore, this study investigated the interaction between the functionalized magnetic NPs and Yersinia enterocolitica wild type (WC-A) using Scanning Electron Microscopy (SEM) and TEM images. In addition, the interaction between MNPs and a Y. enterocolitica mutant strain lacking feroxamine receptor FoxA, was also used to study the binding specificity. The results showed that the capture and isolation of Y. enterocolitica by the MNPs took place in all cases. Moreover, the specific interaction between the MNP conjugate and bacteria did not increase after blocking the free amine groups with t-butoxycarbonyl (Boc) and carboxylic acid (COOH) functional groups. Electrostatic surface interactions instead of molecular recognition between MNP conjugate and feroxamine receptor seem to rule the attachment of bacteria to the conjugate.

Field assessment of bacterial communities and total trihalomethanes: Implications for drinking water networks.

Operation and maintenance (O&M) of drinking water distribution networks (DWDNs) in tropical countries simultaneously face the control of acute and chronic risks due to the presence of microorganisms and disinfection by-products, respectively. In this study, results from a detailed field characterization of microbiological, chemical and infrastructural parameters of a tropical-climate DWDN are presented. Water physicochemical parameters and the characteristics of the network were assessed to evaluate the relationship between abiotic and microbiological factors and their association with the presence of total trihalomethanes (TTHMs). Illumina sequencing of the bacterial 16s rRNA gene revealed significant differences in the composition of biofilm and planktonic communities. The highly diverse biofilm communities showed the presence of methylotrophic bacteria, which suggest the presence of methyl radicals such as THMs within this habitat. Microbiological parameters correlated with water age, pH, temperature and free residual chlorine. The results from this study are necessary to increase the awareness of O&M practices in DWDNs required to reduce biofilm formation and maintain appropriate microbiological and chemical water quality, in relation to biofilm detachment and DBP formation.

Towards sustainable sanitation management: Establishing the costs and willingness to pay for emptying and transporting sludge in rural districts with high rates of access to latrines.

MOTIVATION: Proper management of fecal sludge has significant positive health and environmental externalities. Most research on managing onsite sanitation so far either simulates the costs of, or the welfare effects from, managing sludge in situ in pit latrines. Thus, designing management strategies for onsite rural sanitation is challenging, because the actual costs of transporting sludge for treatment, and sources for financing these transport costs, are not well understood. METHODS: In this paper we calculate the actual cost of sludge management from onsite latrines, and identify the contributions that latrine owners are willing to make to finance the costs. A spreadsheet-based model is used to identify a cost-effective transport option, and to calculate the cost per household. Then a double-bound contingent valuation method is used to elicit from pit-latrine owners their willingness-to-pay to have sludge transported away. This methodology is employed for the case of a rural subdistrict in Bangladesh called Bhaluka, a unit of administration at which sludge management services are being piloted by the Government of Bangladesh. RESULTS: The typical sludge accumulation rate in Bhaluka is calculated at 0.11 liters/person/day and a typical latrine will need to be emptied approximately once every 3 to 4 years. The costs of emptying and transport are high; approximately USD 13 per emptying event (circa 14% of average monthly income); household contributions could cover around 47% of this cost. However, if costs were spread over time, the service would cost USD 4 per year per household, or USD 0.31 per month per household-comparable to current expenditures of rural households on telecommunications. CONCLUSION: This is one of few research papers that brings the costs of waste management together with financing of that cost, to provide evidence for an implementable solution. This framework can be used to identify cost effective sludge management options and private contributions towards that cost in other (context-specific) administrative areas where onsite sanitation is widespread.