Acclimated green microalgae consortium to treat sewage in an alternative urban WWTP in a coastal area of Central Italy.

This study exposed a microalgal consortium formed by Auxenochlorella protothecoides, Tetradesmus obliquus, and Chlamydomonas reinhardtii to six mixed wastewater media containing different proportions of primary (P) or secondary (S) effluents diluted in centrate (C). Algae could grow at centrate concentrations up to 50 %, showing no significant differences between effluents. After acclimation, microalgae cultivated in 50%P-50%C and 50%S-50%C grew at a rate similar to that of control cultures (0.59-0.66 d-1). These results suggest that the consortium acclimated to both sewage streams by modulating the proportion of the species and their metabolism. Acclimation also altered the photosynthetic activity of wastewater-grown samples compared to the control, probably due to partial photoinhibition, changes in consortium composition, and changes in metabolic activity. No major differences were observed between the two streams with respect to biochemical composition, biomass yield, or bioremediation capacity of the cultivated algae but algae grown in the secondary effluent showed qualitatively higher exopolysaccharides (EPS) production than algae grown in primary. Regarding wastewater remediation, microalgae grown in both WW media showed proficient nutrient removal efficiencies (close to 100 %); however, the final pH value (close to 11) would be controversial if the system were upscaled as it is over the legal limit and would cause phosphorus precipitation, so that CO2 addition would be required. The theoretical scale-up of the microalgae system could achieve water treatment costs of 0.109 €·m-3, which was significantly lower than the costs of typical activated sludge systems.

Techno-economic assessment of biorefinery scenarios based on mollusc and fish residuals.

Biorefineries aim to maximise resource recovery from organic sources that have been traditionally considered wastes. In this respect, leftovers from mollusc and seafood processing industries can be a source of multiple bioproducts such as protein hydrolysates (PH), calcium carbonate and co-composted biochar (COMBI). This study aims to evaluate different scenarios of biorefineries fed by mollusc (MW) and fish wastes (FW) to understand which is the most convenient to maximise their profitability. Results showed that the FW-based biorefinery obtained the highest revenues with respect to the amounts of waste treated, i.e., 955.1 €·t-1 and payback period (2.9 years). However, including MW in the biorefinery showed to increase total income as a higher amount of feedstock could be supplied to the system. The profitability of the biorefineries was mainly dependent on the selling price of hydrolysates (considered as 2 €·kg-1 in this study). However, it also entailed the highest operating costs (72.5-83.8% of total OPEX). This highlights the importance of producing high-quality PH in economic and sustainable way to increase the feasibility of the biorefinery.

An overview of operations and processes for circular management of dredged sediments.

Dredging is an essential technique to maintain proper water depths in ports and bays. Many dredged sediments are considered as toxic waste due to their significant amounts of metals and other pollutants. In consequence, they need to be treated to reduce this toxicity and avoid pollutant resuspensions. Physical operations and chemical, thermal and biological processes have been conventionally used to this aim, but the traditional linear sediment approach is often unsustainable and economically and environmentally demanding. Considering the increasing people's awareness in environmental issues, more efficient dredged sediment management schemes are required. Some authors are making significant efforts to improve circularity in sediment management processes by taking advantage of the mineral composition of sediments to obtain products for the building and road construction sectors, therefore decreasing the need of raw materials while reducing the amounts of sediments wasted to landfills. However, information related to the characteristics of these products, their mechanical behaviour and their functionality is still scarce, being sediment-based by-products developed mainly at low Technological Readiness Level (TRL), showing low global impact in the market. To implement circular economy in the dredged sediment sector, some technical and socio-political barriers must be still overcome. To this aim, further research and technological applications must be developed, with the support of decision makers and stakeholders. This review aims at giving an overview of the circular trends applied to toxic dredged sediment management, pointing at current opportunities, barriers and constraints that hinder its wide development.

On-line monitoring of photosynthetic activity based on pH data to assess microalgae cultivation.

Microalgae performance of outdoor cultivation systems is influenced by environmental and operating dynamics. Monitoring and control systems are needed to maximise biomass productivity and nutrient recovery. The goal of this work was to corroborate that pH data could be used to monitor microalgae performance by means of data from an outdoor membrane photobioreactor (MPBR) plant. In this system, microalgae photosynthetic activity was favoured over other physical and biological processes, so that the pH data dynamics was theoretically related to the microalgae carbon uptake rate (CUR). Short- and long-term continuous operations were tested to corroborate the relationship between the first derivate of pH data dynamics (pH') and microalgae photosynthetic activity. Short-term operations showed a good correlation between gross pH' values and MPBR performance. An indicator of the maximum daily average microalgae activity was assessed by a combination of on-line pH' measurements obtained in the long-term and a microalgae growth kinetic model. Both indicators contributed to the development of advanced real-time monitoring and control systems to optimise microalgae cultivation technology.

Nitrite inhibition of microalgae induced by the competition between microalgae and nitrifying bacteria.

Outdoor microalgae cultivation systems treating anaerobic membrane bioreactor (AnMBR) effluents usually present ammonium oxidising bacteria (AOB) competition with microalgae for ammonium uptake, which can cause nitrite accumulation. In literature, nitrite effects over microalgae have shown controversial results. The present study evaluates the nitrite inhibition role in a microalgae-nitrifying bacteria culture. For this purpose, pilot- and lab-scale assays were carried out. During the continuous outdoor operation of the membrane photobioreactor (MPBR) plant, biomass retention time (BRT) of 2 d favoured AOB activity, which caused nitrite accumulation. This nitrite was confirmed to inhibit microalgae performance. Specifically, continuous 5-d lab-scale assays showed a reduction in the nitrogen recovery efficiency by 32, 42 and 80% when nitrite concentration in the culture accounted for 5, 10 and 20 mg N·L-1, respectively. On the contrary, short 30-min exposure to nitrite showed no significant differences in the photosynthetic activity of microalgae under nitrite concentrations of 0, 5, 10 and 20 mg N·L-1. On the other hand, when the MPBR plant was operated at 2.5-d BRT, the nitrite concentration was reduced to negligible values due to increasing activity of microalgae and nitrite oxidising bacteria (NOB). This allowed obtaining maximum MPBR performance; i.e. nitrogen recovery rate (NRR) and biomass productivity of 19.7 ± 3.3 mg N·L-1·d-1 and 139 ± 35 mg VSS·L-1·d-1, respectively; while nitrification rate (NOxR) reached the lowest value (13.5 ± 3.4 mg N·L-1·d-1). Long BRT of 4.5 d favoured NOB growth, avoiding nitrite inhibition. However, it implied a decrease in microalgae growth and the accumulation of nitrate in the MPBR effluent. Hence, it seems that optimum BRT has to be within the range 2-4.5 d in order to favour microalgae growth with respect to AOB and NOB.

Improving membrane photobioreactor performance by reducing light path: operating conditions and key performance indicators.

Microalgae cultivation has been receiving increasing interest in wastewater remediation due to their ability to assimilate nutrients present in wastewater streams. In this respect, cultivating microalgae in membrane photobioreactors (MPBRs) allows decoupling the solid retention time (SRT) from the hydraulic retention time (HRT), which enables to increase the nutrient load to the photobioreactors (PBRs) while avoiding the wash out of the microalgae biomass. The reduction of the PBR light path from 25 to 10 cm increased the nitrogen and phosphorus recovery rates, microalgae biomass productivity and photosynthetic efficiency by 150, 103, 194 and 67%, respectively.The areal biomass productivity (aBP) also increased when the light path was reduced, reflecting the better use of light in the 10-cm MPBR plant. The capital and operating operational expenditures (CAPEX and OPEX) of the 10-cm MPBR plant were also reduced by 27 and 49%, respectively. Discharge limits were met when the 10-cm MPBR plant was operated at SRTs of 3-4.5 d and HRTs of 1.25-1.5 d. At these SRT/HRT ranges, the process could be operated without a high fouling propensity with gross permeate flux (J20) of 15 LMH and specific gas demand (SGDp) between 16 and 20 Nm3air·m-3permeate, which highlights the potential of membrane filtration in MPBRs. When the continuous operation of the MPBR plant was evaluated, an optical density of 680 nm (OD680) and soluble chemical oxygen demand (sCOD) were found to be good indicators of microalgae cell and algal organic matter (AOM) concentrations, while dissolved oxygen appeared to be directly related to MPBR performance. Nitrite and nitrate (NOx) concentration and the soluble chemical oxygen demand:volatile suspended solids ratio (sCOD:VSS) were used as indicators of nitrifying bacteria activity and the stress on the culture, respectively. These parameters were inversely related to nitrogen recovery rates and biomass productivity and could thus help to prevent possible culture deterioration.

Selecting the most suitable microalgae species to treat the effluent from an anaerobic membrane bioreactor.

Conventional treatments for nutrient removal in wastewater are shifting to Anaerobic Membrane Bioreactors, which produce a high-quality effluent with minimum sludge production. The effluent resulting contains high nitrogen and phosphorus load that can be eliminated by microalgae culture. The aim of this study is to evaluate the ammonium and phosphorus removal rate of different microalgae species in the effluent of an anaerobic treatment. For that, 4 different microalgae species have been tested (Chlamydomonas reinhardtii, Scenedesmus obliquus, Chlorella vulgaris and Monoraphidium braunii) in batch monoculture and mixed conditions. Results indicate that all species are able to eliminate both P and N in the medium with high removal rates. However, a slight interspecies competition may boost these removal rates and productivity values ensuring, the success of the process.

Continuous 3-year outdoor operation of a flat-panel membrane photobioreactor to treat effluent from an anaerobic membrane bioreactor.

A membrane photobioreactor (MPBR) plant was operated continuously for 3 years to evaluate the separate effects of different factors, including: biomass and hydraulic retention times (BRT, HRT), light path (Lp), nitrification rate (NOxR), nutrient loading rates (NLR, PLR) and others. The overall effect of all these parameters which influence MPBR performance had not previously been assessed. The multivariate projection approach chosen for this study provided a good description of the collected data and facilitated their visualisation and interpretation. Forty variables used to control and assess MPBR performance were evaluated during three years of continuous outdoor operation by means of principal component analysis (PCA) and partial least squares (PLS) analysis. The PCA identified the photobioreactor (PBR) light path as the factor with the largest influence on data variability. Other important factors were: nitrogen and phosphorus recovery rates (NRR, PRR), biomass productivity (BP), optical density of 680 nm (OD680), ammonium and phosphorus effluent concentration (NH4, P), HRT, BRT, air flow rate (Fair) and nitrogen and phosphorus loading rates (NLR and PLR). The MPBR performance could be adequately estimated by a PLS model based on all the recorded variables, but this estimation worsened appreciably when only the controlled variables (Lp, Fair, HRT and BRT) were used as predictors, which underlines the importance of the non-controlled variables on MPBR performance. The microalgae cultivation process could thus only be partially controlled by the design and operating variables. A high nitrification rate was found to be inadvisable, since it showed an inverse correlation with NRR. In this respect, temperature and microalgae biomass concentration appeared to be the main factors to mitigate nitrifying bacteria activity.

Preliminary data set to assess the performance of an outdoor membrane photobioreactor.

This data in brief (DIB) article is related to a Research article entitled 'Optimising an outdoor membrane photobioreactor for tertiary sewage treatment' [1]. Data related to the effect of substrate turbidity, the ammonium concentration at which the culture reaches nitrogen-deplete conditions and the microalgae growth rate under outdoor conditions is provided. Microalgae growth rates under different substrate turbidity were obtained to assess the reduction of the culture's light availability. Lab-scale experiments showed growth rates reductions of 22-44%. Respirometric tests were carried to know the limiting ammonium concentration in this microalgae-based wastewater treatment system. Growth rates (µ) of green microalgae Scenedesmus and Chlorella obtained under outdoor conditions; i.e. 0.40 d-1 (R2 = 0.993) and 0.43 d-1 (R2 = 0.995), respectively, can be useful to obtain optimum operating conditions of membrane photobioreactor (MPBR).

Dataset to assess the shadow effect of an outdoor microalgae culture.

This data in brief (DIB) article is related to a Research article [1]. Microalgae biomass absorb the light photons that are supplied to the culture, reducing the light availability in the inner parts of the photobioreactors. This is known as self-shading or shadow effect. This effect has been widely studied in lab conditions, but information about self-shading in outdoor photobioreactors is scarce. How this shadow effect affects the light availability in an outdoor photobioreactor was evaluated. In addition, advantages and disadvantages of different artificial light sources which can overcome light limitation are described.

Effect of ambient temperature variations on an indigenous microalgae-nitrifying bacteria culture dominated by Chlorella.

Two outdoor photobioreactors were operated to evaluate the effect of variable ambient temperature on an indigenous microalgae-nitrifying bacteria culture dominated by Chlorella. Four experiments were carried out in different seasons, maintaining the temperature-controlled PBR at around 25 °C (by either heating or cooling), while the temperature in the non-temperature-controlled PBR was allowed to vary with the ambient conditions. Temperatures in the range of 15-30 °C had no significant effect on the microalgae cultivation performance. However, when the temperature rose to 30-35 °C microalgae viability was significantly reduced. Sudden temperature rises triggered AOB growth in the indigenous microalgae culture, which worsened microalgae performance, especially when AOB activity made the system ammonium-limited. Microalgae activity could be recovered after a short temperature peak over 30 °C once the temperature dropped, but stopped when the temperature was maintained around 28-30 °C for several days.

Optimising an outdoor membrane photobioreactor for tertiary sewage treatment.

The operation of an outdoor membrane photobioreactor plant which treated the effluent of an anaerobic membrane bioreactor was optimised. Biomass retention times of 4.5, 6, and 9 days were tested. At a biomass retention time of 4.5 days, maximum nitrogen recovery rate:light irradiance ratios, photosynthetic efficiencies and carbon biofixations of 51.7 ±â€¯14.3 mg N·mol-1, 4.4 ±â€¯1.6% and 0.50 ±â€¯0.05 kg CO2·m3influent, respectively, were attained. Minimum membrane fouling rates were achieved when operating at the shortest biomass retention time because of the lower solid concentration and the negligible amount of cyanobacteria and protozoa. Hydraulic retention times of 3.5, 2, and 1.5 days were tested at the optimum biomass retention times of 4.5 days under non-nutrient limited conditions, showing no significant differences in the nutrient recovery rates, photosynthetic efficiencies and membrane fouling rates. However, nitrogen recovery rate:light irradiance ratios and photosynthetic efficiency significantly decreased when hydraulic retention time was further shortened to 1 day, probably due to a rise in the substrate turbidity which reduced the light availability in the culture. Optimal carbon biofixations and theoretical energy recoveries from the biomass were obtained at hydraulic retention time of 3.5 days, which accounted for 0.55 ±â€¯0.05 kg CO2·m-3influent and 0.443 ±â€¯0.103 kWh·m-3influent, respectively.

Resource recovery from sulphate-rich sewage through an innovative anaerobic-based water resource recovery facility (WRRF).

This research work proposes an innovative water resource recovery facility (WRRF) for the recovery of energy, nutrients and reclaimed water from sewage, which represents a promising approach towards enhanced circular economy scenarios. To this aim, anaerobic technology, microalgae cultivation, and membrane technology were combined in a dedicated platform. The proposed platform produces a high-quality solid- and coliform-free effluent that can be directly discharged to receiving water bodies identified as sensitive areas. Specifically, the content of organic matter, nitrogen and phosphorus in the effluent was 45 mg COD·L-1, 14.9 mg N·L-1 and 0.5 mg P·L-1, respectively. Harvested solar energy and carbon dioxide biofixation in the form of microalgae biomass allowed remarkable methane yields (399 STP L CH4·kg-1 CODinf) to be achieved, equivalent to theoretical electricity productions of around 0.52 kWh per m3 of wastewater entering the WRRF. Furthermore, 26.6% of total nitrogen influent load was recovered as ammonium sulphate, while nitrogen and phosphorus were recovered in the biosolids produced (650 ± 77 mg N·L-1 and 121.0 ± 7.2 mg P·L-1).

Outdoor flat-panel membrane photobioreactor to treat the effluent of an anaerobic membrane bioreactor. Influence of operating, design, and environmental conditions.

As microalgae have the ability to simultaneously remove nutrients from wastewater streams while producing valuable biomass, microalgae-based wastewater treatment is a win-win strategy. Although recent advances have been made in this field in lab conditions, the transition to outdoor conditions on an industrial scale must be further investigated. In this work an outdoor pilot-scale membrane photobioreactor plant was operated for tertiary sewage treatment. The effects of different parameters on microalgae performance were studied including: temperature, light irradiance (solar and artificial irradiance), hydraulic retention time (HRT), biomass retention time (BRT), air sparging system and influent nutrient concentration. In addition the competition between microalgae and ammonium oxidising bacteria for ammonium was also evaluated. Maximum nitrogen and phosphorus removal rates of 12.5 ± 4.2 mgN·L-1·d-1 and 1.5 ± 0.4 mgP·L-1·d-1, respectively, were achieved at a BRT of 4.5 days and HRT of 2.5 days, while a maximum biomass productivity of 78 ± 13 mgVSS·L-1·d-1 (VSS: volatile suspended solids) was reached. While the results obtained so far are promising, they need to be improved to make the transition to industrial scale operations feasible.

Wastewater nutrient removal in a mixed microalgae-bacteria culture: effect of light and temperature on the microalgae-bacteria competition.

The aim of this study was to evaluate the effect of light intensity and temperature on nutrient removal and biomass productivity in a microalgae-bacteria culture and their effects on the microalgae-bacteria competition. Three experiments were carried out at constant temperature and various light intensities: 40, 85 and 125 µE m-2 s-1. Other two experiments were carried out at variable temperatures: 23 ± 2°C and 28 ± 2°C at light intensity of 85 and 125 µE m-2 s-1, respectively. The photobioreactor was fed by the effluent from an anaerobic membrane bioreactor. High nitrogen and phosphorus removal efficiencies (about 99%) were achieved under the following operating conditions: 85-125 µE m-2 s-1 and 22 ± 1°C. In the microalgae-bacteria culture studied, increasing light intensity favoured microalgae growth and limited the nitrification process. However, a non-graduated temperature increase (up to 32°C) under the light intensities studied caused the proliferation of nitrifying bacteria and the nitrite and nitrate accumulation. Hence, light intensity and temperature are key parameters in the control of the microalgae-bacteria competition. Biomass productivity significantly increased with light intensity, reaching 50.5 ± 9.6, 80.3 ± 6.5 and 94.3 ± 7.9 mgVSS L-1 d-1 for a light intensity of 40, 85 and 125 µE m-2 s-1, respectively.

Short and long-term experiments on the effect of sulphide on microalgae cultivation in tertiary sewage treatment.

Microalgae cultivation appears to be a promising technology for treating nutrient-rich effluents from anaerobic membrane bioreactors, as microalgae are able to consume nutrients from sewage without an organic carbon source, although the sulphide formed during the anaerobic treatment does have negative effects on microalgae growth. Short and long-term experiments were carried out on the effects of sulphide on a mixed microalgae culture. The short-term experiments showed that the oxygen production rate (OPR) dropped as sulphide concentration increased: a concentration of 5mgSL-1 reduced OPR by 43%, while a concentration of 50mgSL-1 came close to completely inhibiting microalgae growth. The long-term experiments revealed that the presence of sulphide in the influent had inhibitory effects at sulphide concentrations above 20mgSL-1 in the culture, but not at concentrations below 5mgSL-1. These conditions favoured Chlorella growth over that of Scenedesmus.

Water quality of Danube Delta systems: ecological status and prediction using machine-learning algorithms.

Environmental issues have a worldwide impact on water bodies, including the Danube Delta, the largest European wetland. The Water Framework Directive (2000/60/EC) implementation operates toward solving environmental issues from European and national level. As a consequence, the water quality and the biocenosis structure was altered, especially the composition of the macro invertebrate community which is closely related to habitat and substrate heterogeneity. This study aims to assess the ecological status of Southern Branch of the Danube Delta, Saint Gheorghe, using benthic fauna and a computational method as an alternative for monitoring the water quality in real time. The analysis of spatial and temporal variability of unicriterial and multicriterial indices were used to assess the current status of aquatic systems. In addition, chemical status was characterized. Coliform bacteria and several chemical parameters were used to feed machine-learning (ML) algorithms to simulate a real-time classification method. Overall, the assessment of the water bodies indicated a moderate ecological status based on the biological quality elements or a good ecological status based on chemical and ML algorithms criteria.

First Report of 'Candidatus Liberibacter asiaticus' Associated with Citrus Huanglongbing in the Dominican Republic.

In August 2008, unusual symptoms were observed in Mexican lime trees (Citrus aurantifolia (Christm.) Swing) in the municipality of Luperón, province of Puerto Plata on the north coast of the Dominican Republic. Symptoms observed in young and old trees included blotchy mottle on leaves, healthy-appearing larger branches with smaller side branches that displayed chlorotic leaves, abscised and lopsided fruit, and branch dieback, all symptoms similar to those of citrus huanglongbing associated with 'Candidatus Liberibacter' spp. (1). Symptoms were observed in an area of ~100 ha surrounding Luperón, where Mexican lime trees were grown as seedlings and no commercial plantings of other citrus were present. Symptomatic leaves were collected from 16 trees in September 2008, and DNA was extracted from petioles and midveins with a DNeasy kit (Qiagen, Gaithersburg, MD) or with chloroform/isoamyl alcohol (24:1). Real-time PCR with the16S rDNA primer/probe set specific to 'Ca. Liberibacter asiaticus' and performed as described (2) gave Ct values comparable with the positive control for five samples. Conventional PCR with the forward (5'-tcgagcgcgtatgcaatacg-3') and reverse (5'-ctacctttttctacgggataacgc-3') primers used in real-time PCR (2) amplified a 75-bp product from these five samples. Eleven to twelve clones were sequenced from each sample and BLAST analysis of a consensus sequence for each sample (GenBank Accession Nos. FJ489643-FJ489647) showed 98% (e.g., EU921622, EU921618) to 100% identity (e.g., FJ236554, FJ263702) with 16S rDNA sequences of 'Ca. Liberibacter asiaticus'. A larger 912-bp portion of the 16S rDNA gene was amplified from each sample by conventional PCR with sense (5'-gagcctaccaaggctacgat-3') and antisense (5'-gcgttatcccgtagaaaaaggtag-3') primers designed from the sequence of 'Ca. Liberibacter asiaticus' strain LJZ-4730 (GenBank Accession No. FJ263700). Nine to twelve clones were sequenced for each sample and BLAST analysis of a consensus sequence for each sample (GenBank Accession Nos. FJ811891-FJ811895) showed 100% identity to 'Ca. Liberibacter asiaticus' (DQ471900, DQ4719010) from Florida and Brazil, respectively. To confirm this identification, 693 bp of the outer membrane protein gene (omp) were amplified from each of the five positive samples by conventional PCR using sense (5'-gtgattctgagggtgagcg-3') and antisense (5'-cgaactcactgagaactgatc-3') primers designed from nucleotides 15 to 33 and 687 to 707, respectively, of the omp gene from 'Ca. Liberibacter asiaticus' strain MZ (GenBank Accession No. EF580135). The consensus sequences from 12 clones from each sample (GenBank Accession Nos. FJ489638-FJ489642) showed 99% (e.g., FJ236564, AY842429) to 100% (e.g., FJ236566, EF580135) nucleotide identity and the predicted translation product showed 100% amino acid identity (e.g., AAX47433, AAX47431) with the omp gene from 'Ca. Liberibacter asiaticus'. These results confirm the presence of and to our knowledge, this is the first report of 'Ca. Liberibacter asiaticus' in the Dominican Republic. Huanglongbing is a destructive disease of citrus (1) and its spread is expected to adversely affect citrus production in the Dominican Republic with subsequent negative effects predicted for the employment of thousands of people. References: (1) J. M. Bové, J. Plant Pathol. 88:7, 2006. (2) W. Li et al. J. Microbiol. Methods 66:104, 2006.