Gutierrez, R.; Ferrer, I.; González-Molina, A.; Salvado, H.; Garcia, J.; Uggetti, E. Water research (Oxford) Vol. 106, p. 539-549 DOI: 10.1016/j.watres.2016.10.039 Data de publicació: 2016-12 Article en revista
Microalgal biomass harvesting by inducing spontaneous flocculation (bioflocculation) sets an attractive approach, since neither chemicals nor energy are needed. Indeed, bioflocculation may be promoted by recycling part of the harvested microalgal biomass to the photobioreactor in order to increase the predominance of rapidly settling microalgae species. The aim of the present study was to improve the recovery of microalgal biomass produced in wastewater treatment high rate algal ponds (HRAPs) by recycling part of the harvested microalgal biomass. The recirculation of 2% and 10% (dry weight) of the HRAPs microalgal biomass was tested over one year in an experimental HRAP treating real urban wastewater. Results indicated that biomass recycling had a positive effect on the harvesting efficiency, obtaining higher biomass recovery in the HRAP with recycling (R-HRAP) (92–94%) than in the control HRAP without recycling (C-HRAP) (75–89%). Microalgal biomass production was similar in both systems, ranging between 3.3 and 25.8 g TSS/m2d, depending on the weather conditions. Concerning the microalgae species, Chlorella sp. was dominant overall the experimental period in both HRAPs (abundance >60%). However, when the recycling rate was increased to 10%, Chlorella sp. dominance decreased from 97.6 to 88.1%; while increasing the abundance of rapidly settling species such as Stigeoclonium sp. (16.8%, only present in the HRAP with biomass recycling) and diatoms (from 0.7 to 7.3%). Concerning the secondary treatment of the HRAPs, high removals of COD (80%) and N-NH4+ (97%) were found in both HRAPs. Moreover, by increasing the biomass recovery in the R-HRAP the effluent total suspended solids (TSS) concentration was decreased to less than 35 mg/L, meeting effluent quality requirements for discharge. This study shows that microalgal biomass recycling (10% dry weight) increases biomass recovery up to 94% by selecting the most rapidly settling microalgae species without compromising the biomass production and improving the wastewater treatment in terms of TSS removal.
Degradation of emerging organic compounds in saturated porous media is usually postulated as following simple low-order models. This is a strongly oversimplified, and in some cases plainly incorrect model, that does not consider the fate of the different metabolites. Furthermore, it does not account for the reversibility in the reaction observed in a few emerging organic compounds, where the parent is recovered from the metabolite. One such compound is the antibiotic sulfamethoxazole (SMX). In this paper, we first compile existing experimental data to formulate a complete model for the degradation of SMX in aquifers subject to varying redox conditions, ranging from aerobic to iron reducing. SMX degrades reversibly or irreversibly to a number of metabolites that are specific of the redox state. Reactions are in all cases biologically mediated. We then propose a mathematical model that reproduces the full fate of dissolved SMX subject to anaerobic conditions and that can be used as a first step in emerging compound degradation modeling efforts. The model presented is tested against the results of the batch experiments of Barbieri et al. (2012) and Nödler et al. (2012) displaying a non-monotonic concentration of SMX as a function of time under denitrification conditions, as well as those of Mohatt et al. (2011), under iron reducing conditions.
Reverse osmosis (RO) membrane exposure to bisulphite, chlorite, bromide and iron(III) was assessed in terms of membrane composition, structure and performance. Membrane composition was determined by Rutherford backscattering spectrometry (RBS) and membrane performance was assessed by water and chloride permeation, using a modified version of the solution-diffusion model. Iron(III) dosage in presence of bisulphite led to an autooxidation of the latter, probably generating free radicals which damaged the membrane. It comprised a significant raise in chloride passage (chloride permeation coefficient increased 5.3–5.1 fold compared to the virgin membrane under the conditions studied) rapidly. No major differences in terms of water permeability and membrane composition were observed. Nevertheless, an increase in the size of the network pores, and a raise in the fraction of aggregate pores of the polyamide (PA) layer were identified, but no amide bond cleavage was observed. These structural changes were therefore, in accordance with the transport properties observed.
Guimera, X.; Dorado, A.D.; Bonsfills, A.; Gabriel Buguña, Gemma; Gabriel, D.; Gamisans, X. Water research (Oxford) Vol. 102, p. 551-560 DOI: 10.1016/j.watres.2016.07.009 Data de publicació: 2016-07-07 Article en revista
Knowledge of mass transport mechanisms in biofilm-based technologies such as biofilters is essential to improve bioreactors performance by preventing mass transport limitation. External and internal mass transport in biofilms was characterized in heterotrophic biofilms grown on a flat plate bioreactor. Mass transport resistance through the liquid-biofilm interphase and diffusion within biofilms were quantified by in situ measurements using microsensors with a high spatial resolution (<50 mm). Experimental conditions were selected using a mathematical procedure based on the Fisher Information Matrix to increase the reliability of experimental data and minimize confidence intervals of estimated mass transport coefficients. The sensitivity of external and internal mass transport resistances to flow conditions within the range of typical fluid velocities over biofilms (Reynolds numbers between 0.5 and 7) was assessed. Estimated external mass transfer coefficients at different liquid phase flow velocities showed discrepancies with studies considering laminar conditions in the diffusive boundary layer near the liquid-biofilm interphase. The correlation of effective diffusivity with flow velocities showed that the heterogeneous structure of biofilms defines the transport mechanisms inside biofilms. Internal mass transport was driven by diffusion through cell clusters and aggregates at Re below 2.8. Conversely, mass transport was driven by advection within pores, voids and water channels at Re above 5.6. Between both flow velocities, mass transport occurred by a combination of advection and diffusion. Effective diffusivities estimated at different biofilm densities showed a linear increase of mass transport resistance due to a porosity decrease up to biofilm densities of 50 g VSS$L1. Mass transport was strongly limited at higher biofilm densities. Internal mass transport results were used to propose an empirical correlation to assess the effective diffusivity within biofilms considering the influence of hydrodynamics and biofilm density.
Mora, M.; Lopez, L.; Lafuente Sancho, Francisco Javier; Pérez, J.; Kleerebezem, R.; van Loosdrecht , M.; Gamisans, X.; Gabriel, D. Water research (Oxford) Vol. 89, p. 282-292 DOI: 10.1016/j.watres.2015.11.061 Data de publicació: 2016-02-01 Article en revista
Respirometry was used to reveal the mechanisms involved in aerobic biological sulfide oxidation and to characterize the kinetics and stoichiometry of a microbial culture obtained from a desulfurizing biotrickling filter. Physical–chemical processes such as stripping and chemical oxidation of hydrogen sulfide were characterized since they contributed significantly to the conversions observed in respirometric tests. Mass transfer coefficient for hydrogen sulfide and the kinetic parameters for chemical oxidation of sulfide with oxygen were estimated. The stoichiometry of the process was determined and the different steps in the sulfide oxidation process were identified. The conversion scheme proposed includes intermediate production of elemental sulfur and thiosulfate and the subsequent oxidation of both compounds to sulfate. A kinetic model describing each of the reactions observed during sulfide oxidation was calibrated and validated. The product selectivity was found to be independent of the dissolved oxygen to hydrogen sulfide concentration ratio in the medium at sulfide concentrations ranging from 3 to 30 mg S L-1. Sulfide was preferentially consumed (SOURmax = 49.2 mg DO g-1 VSS min-1) and oxidized to elemental sulfur at dissolved oxygen concentrations above 0.8 mg DO L-1. Substrate inhibition of sulfide oxidation was observed (Ki,S2- = 42.4 mg S L-1). Intracellular sulfur accumulation also affected negatively the sulfide oxidation rate. The maximum fraction of elemental sulfur accumulated inside cells was estimated (25.6% w/w) and a shrinking particle equation was included in the kinetic model to describe elemental sulfur oxidation. The microbial diversity obtained through pyrosequencing analysis revealed that Thiothrix sp. was the main species present in the culture (>95%).
Sales of bottled drinking water have shown a large growth during the last two decades due to the general belief that this kind of water is healthier, its flavour is better and its consumption risk is lower than that of tap water. Due to the previous points, consumers are more demanding with bottled mineral water, especially when dealing with its organoleptic properties, like taste and odour. This work studies the compounds that can generate obnoxious smells, and that consumers have described like swampy, rotten eggs, sulphurous, cooked vegetable or cabbage. Closed loop stripping analysis (CLSA) has been used as a pre-concentration method for the analysis of off-flavour compounds in water followed by identification and quantification by means of GC-MS. Several bottled water with the aforementioned smells showed the presence of volatile dimethyl selenides and dimethyl sulphides, whose concentrations ranged, respectively, from 4 to 20 ng/L and from 1 to 63 ng/L. The low odour threshold concentrations (OTCs) of both organic selenide and sulphide derivatives prove that several objectionable odours in bottled waters arise from them. Microbial loads inherent to water sources, along with some critical conditions in water processing, could contribute to the formation of these compounds. There are few studies about volatile organic compounds in bottled drinking water and, at the best of our knowledge, this is the first study reporting the presence of dimethyl selenides and dimethyl sulphides causing odour problems in bottled waters
This work aimed at determining the amount of energy that can be harvested by implementing microbial fuel cells (MFC) in horizontal subsurface constructed wetlands (HSSF CWs) during the treatment of real domestic wastewater. To this aim, MFC were implemented in a pilot plant based on two HSSF CW, one fed with primary settled wastewater (Settler line) and the other fed with the effluent of a hydrolytic upflow sludge blanket reactor (HUSB line). The eubacterial and archaeal community was profiled on wetland gravel, MFC electrodes and primary treated wastewater by means of 16S rRNA gene-based 454-pyrosequencing and qPCR of 16S rRNA and mcrA genes. Maximum current (219 mA/m(2)) and power (36 mW/m(2)) densities were obtained for the HUSB line. Power production pattern correlated well with water level fluctuations within the wetlands, whereas the type of primary treatment implemented had a significant impact on the diversity and relative abundance of eubacteria communities colonizing MFC. It is worth noticing the high predominance (13-16% of relative abundance) of one OM belonging to Geobacter on active MFC of the HUSB line that was absent for the settler line MFC. Hence, MFC show promise for power production in constructed wetlands receiving the effluent of a HUSB reactor. (C) 2015 Elsevier Ltd. All rights reserved.
Microalgal biomass grown in wastewater treatment raceway ponds may be valorised producing bioenergy through anaerobic digestion. However, pretreatment techniques seem to be necessary for enhancing microalgae methane yield. In this study, hydrothermal pretreatment was studied prior to batch and continuous reactors. The pretreatment increased organic matter solubilisation (8-13%), anaerobic digestion rate (30-90%) and final methane yield (17-39%) in batch tests. The highest increase was attained with the pretreatment at 130 degrees C for 15 min, which was attested in a laboratory-scale continuous reactor operated at a hydraulic retention time of 20 days with an average organic loading rate of 0.7 g VS/L center dot day. The methane yield increased from 0.12 to 0.17 L CH4/g VS (41%) in the pretreated digester as compared to the control. Microscopic images of microalgal biomass showed that pretreated cells had unstructured organelles and disrupted cell wall external layer, which may enhance the hydrolysis. Indeed, images of the pretreated reactor digestate showed how cells were more degraded than in the control reactor. (C) 2014 Elsevier Ltd. All rights reserved.
Adrados, B.; Sánchez, O.; Arias, C.; Bécares, E.; Garrido Beltrán, L.; Mas, J.; Brix, H.; Morato, J. Water research (Oxford) Vol. 55, p. 304-312 DOI: 10.1016/j.watres.2014.02.011 Data de publicació: 2014-05-15 Article en revista
The prokaryotic microbial communities (Bacteria and Archaea) of three different systems operating in Denmark for the treatment of domestic wastewater (horizontal flow constructed wetlands (HFCW), vertical flow constructed wetlands (VFCW) and biofilters (BF)) was analysed using endpoint PCR followed by Denaturing Gradient Gel Electrophoresis (DGGE). Further sequencing of the most representative bacterial bands revealed that diverse and distinct bacterial communities were found in each system unit, being gamma-Proteobacteria and Bacteroidetes present mainly in all of them, while Firmicutes was observed in HFCW and BF. Members of the Actinobacteria group, although found in HFCW and VFCW, seemed to be more abundant in BF units. Finally, some representatives of alpha, beta and delta-Proteobacteria, Acidobacteria and Chloroflexi were also retrieved from some samples. On the other hand, a lower archaeal diversity was found in comparison with the bacterial population. Cluster analysis of the DGGE bacterial band patterns showed that community structure was related to the design of the treatment system and the organic matter load, while no clear relation was established between the microbial assemblage and the wastewater influent. (C) 2014 Elsevier Ltd. All rights reserved.
This paper describes the anaerobic digestion of microalgal biomass from high rate ponds in continuous anaerobic reactors for biogas production. With hydraulic retention times (HRT) of 15 and 20 days, the volatile solids (VS) removal did not exceed 30%, and the methane production rate ranged between 0.12 and 0.14 L CH4/L day. To improve process performance, microwave irradiation at 900 W for 3 min (specific energy similar to 70,000 kJ/kg VS) was applied as a pretreatment step. The VS removal increased to 40 and 45% at 15 and 20 days HRT, respectively. Consequently, the methane production rate increased to 0.16 and 0.20 L CH4/L day at 15 and 20 days HRT, respectively. Microscopic analysis confirmed cell wall damage, although generally without lysis, after irradiating microalgal biomass. However, the energy consumption was much higher than the extra energy production of the process. Indeed, microalgal biomass should not only be thickened but also dewatered if microwave irradiation was to be applied as a pretreatment to anaerobic digestion for biogas production. (C) 2013 Elsevier Ltd. All rights reserved.
Gibert, O.; Lefèvre, B.; Fernández, M.; Bernat, X.; Paraira, M.; Pons, M. Water research (Oxford) Vol. 47, num. 8, p. 2821-2829 DOI: 10.1016/j.watres.2013.02.028 Data de publicació: 2013-03-15 Article en revista
The removal of natural organic matter (NOM) and, more particularly, its individual fractions by two different GACs was investigated in full-scale filters in a drinking water treatment plant (DWTP). Fractionation of NOM was performed by high performance size exclusion chromatography (HPSEC) into biopolymers, humic substances, building blocks and low molecular weight organics. The sorption capacity of GAC in terms of iodine number (IN) and apparent surface area (SBET), as well as the filling of narrow- and super-microporosity were monitored over the 1-year operation of the filters. Both GACs demonstrated to be effective at removing NOM over a wide range of fractions, especially the low and intermediate molecular weight fractions. TOC removal initially occurred via adsorption, and smaller (lighter) fractions were more removed as they could enter and diffuse more easily through the pores of the adsorbent.
The removal of natural organic matter (NOM) and, more particularly, its individual fractions by two different GACs was investigated in full-scale filters in a drinking water treatment plant (DWTP). Fractionation of NOM was performed by high performance size exclusion chromatography (HPSEC) into biopolymers, humic substances, building blocks and low molecular weight organics. The sorption capacity of GAC in terms of iodine number (IN) and apparent surface area (SBET), as well as the filling of narrow- and super-microporosity were monitored over the 1-year operation of the filters. Both GACs demonstrated to be effective at removing NOM over a wide range of fractions, especially the low and intermediate molecular weight fractions. TOC removal initially occurred via adsorption, and smaller (lighter) fractions were more removed as they could enter and diffuse more easily through the pores of the adsorbent. As time progressed, biodegradation also played a role in the TOC removal, and lighter fractions continued to be preferentially removed due to their higher biodegradability. The gained knowledge would assist drinking water utilities in selecting a proper GAC for the removal of NOM from water and, therefore, complying more successfully the latest water regulations.
Pedescoll, A.; Sidrach, A.; Sánchez, J.C.; Carretero, J.; Marianna Garfi'; Bécares, E. Water research (Oxford) Vol. 47, num. 3, p. 1448-1458 DOI: 10.1016/j.watres.2012.12.010 Data de publicació: 2013-03-01 Article en revista
The aim of this study was to evaluate the effect of different horizontal constructed wetland (CW) design parameters on solids distribution, loss of hydraulic conductivity over time and hydraulic behaviour, in order to assess clogging processes in wetlands. For this purpose, an experimental plant with eight CWs was built at mesocosm scale. Each CW presented a different design characteristic, and the most common CW configurations were all represented: free water surface flow (FWS) with different effluent pipe locations, FWS with floating macrophytes and subsurface flow (SSF), and the presence of plants and specific species (Typha angustifolia and Phragmites australis) was also considered. The loss of the hydraulic conductivity of gravel was greatly influenced by the presence of plants and organic load (representing a loss of 20% and c.a. 10% in planted wetlands and an overloaded system, respectively). Cattail seems to have a greater effect on the development of clogging since its below-ground biomass weighed twice as much as that of common reed. Hydraulic behaviour was greatly influenced by the presence of a gravel matrix and the outlet pipe position. In strict SSF CW, the water was forced to cross the gravel and tended to flow diagonally from the top inlet to the bottom outlet (where the inlet and outlet pipes were located). However, when FWS was considered, water preferentially flowed above the gravel, thus losing half the effective volume of the system. Only the presence of plants seemed to help the water flow partially within the gravel matrix.
Gibert, O.; Lefèvre, B.; Fernández, M.; Bernat, X.; Paraira, M.; Calderer, M.; Martinez, X. Water research (Oxford) Vol. 47, num. 3, p. 1101-1110 DOI: 10.1016/j.watres.2012.11.026 Data de publicació: 2013-03-01 Article en revista
Under normal operation conditions, granular activated carbon (GAC) employed in drinking water treatment plants (DWTPs) for natural organic matter (NOM) removal can be colonised by microorganisms which can eventually establish active biofilms. The formation of such biofilms can contribute to NOM removal by biodegradation, but also in clogging phenomena that can make necessary more frequent backwashes. Biofilm occurrence and evolution under full-scale-like conditions (i.e. including periodic backwashing) are still uncertain, and GAC filtration is usually operated with a strong empirical component. The aim of the present study was to assess the formation and growth, if any, of biofilm in a periodically backwashed GAC filter. For this purpose, an on-site pilot plant was assembled and operated to closely mimic the GAC filters installed in the DWTP in Sant Joan Despi (Barcelona, Spain). The study comprised a monitoring of both water and GAC cores withdrawn at various depths and times throughout 1 year operation....
Under normal operation conditions, granular activated carbon (GAC) employed in drinking water treatment plants (DWTPs) for natural organic matter (NOM) removal can be colonised by microorganisms which can eventually establish active biofilms. The formation of such biofilms can contribute to NOM removal by biodegradation, but also in clogging phenomena that can make necessary more frequent backwashes. Biofilm occurrence and evolution under full-scale-like conditions (i.e. including periodic backwashing) are still uncertain, and GAC filtration is usually operated with a strong empirical component. The aim of the present study was to assess the formation and growth, if any, of biofilm in a periodically backwashed GAC filter. For this purpose, an on-site pilot plant was assembled and operated to closely mimic the GAC filters installed in the DWTP in Sant Joan Despí (Barcelona, Spain). The study comprised a monitoring of both water and GAC cores withdrawn at various depths and times throughout 1 year operation. The biomass parameters assessed were total cell count by confocal laser scanning microscopy (CLSM), DNA and adenosine triphosphate (ATP). Visual examination of GAC particles was also conducted by high-resolution field emission scanning electron microscopy (FESEM). Additionally, water quality and GAC surface properties were monitored. Results provided insight into the extent and spatial distribution of biofilm within the GAC bed. To sum up, it was found that backwashing could physically detach bacteria from the biofilm, which could however build back up to its pre-backwashing concentration before next backwashing cycle.
This study aimed at assessing the influence of primary treatment (hydrolytic upflow sludge blanket (HUSB) reactor vs. conventional settling) and operational strategy (alternation of saturated/ unsaturated phases vs. permanently saturated) on the removal of various
emerging organic contaminants (i.e. ibuprofen, diclofenac, acetaminophen, tonalide, oxybenzone, bisphenol A) in horizontal subsurface flow constructed wetlands. For that purpose, a continuous injection experiment was carried out in an experimental treatment plant for 26 days. The plant had 3 treatment lines: a control line (settler-wetland permanently
saturated), a batch line (settler-wetland operated with saturate/unsaturated phases)
and an anaerobic line (HUSB reactor-wetland permanently saturated). In each line,
wetlands had a surface area of 2.95 m2, a water depth of 25 cm and a granular medium
D60 ¼ 7.3 mm, and were planted with common reed. During the study period the wetlands
were operated at a hydraulic and organic load of 25 mm/d and about 4.7 g BOD/m2d,
respectively. The injection experiment delivered very robust results that show how the occurrence of higher redox potentials within the wetland bed promotes the elimination of conventional quality parameters as well as emerging microcontaminants. Overall, removal
efficiencies were always greater for the batch line than for the control and anaerobic lines, and to this respect statistically significantly differences were found for ibuprofen, diclofenac,
oxybenzone and bisphenol A. As an example, ibuprofen, whose major removal mechanism has been reported to be biodegradation under aerobic conditions, showed a higher removal in the batch line (85%) than in the control (63%) and anaerobic (52%) lines.
Bisphenol A showed also a great dependence on the redox status of the wetlands, finding
an 89% removal rate for the batch line, as opposed to the control and anaerobic lines
(79 and 65%, respectively). Furthermore, diclofenac showed a greater removal under
a higher redox status (70, 48 and 32% in the batch, control and anaerobic lines). Average
removal efficiencies of acetaminophen, oxybenzone and tonalide were almost >90% for the 3 treatment lines. The results of this study indicate that the efficiency of horizontal flow constructed wetland systems can be improved by using a batch operation strategy.
The impact of LCFA adsorption on the methanogenic activity was evaluated in batch assays for two anaerobic granular sludges in the presence and absence of bentonite as synthetic adsorbent. A clear inhibitory effect at an oleate (C18:1) concentration of 0.5 gC18:1 L-1 was observed for both sludges.
The effects of design and operational factors on the dynamics of ciliated protozoa in constructed wetlands (CWs) treating wastewater remain poorly known, although bacterivory by ciliates could have important implications for nutrient cycling in these systems. We conducted a greenhouse experiment with eight wetland mesocosms (1 m2) fed with synthetic wastewater to assess how macrophyte species (Phragmites australis, Phalaris arundinacea, and Typha angustifolia), location within CW (longitudinal, depth), and temporal fluctuations affect ciliate abundance and diversity. Urosoma similis was the most abundant taxon, but Hypotrichidae, Scuticociliates, Drepomonas revoluta, and Acineria uncinata were also abundant. Longitudinal location had the highest impact on ciliate dynamics, with more abundant and diverse communities in the initial section of wetlands. P. australis/T. angustifolia and P. arundinacea had the most and least favorable conditions for ciliates, respectively, but differences among macrophytes were mostly not significant. Ciliate abundance appeared to decline from August to November, most likely because of lower temperature and plant inputs of organic matter and oxygen. Depth had no apparent impact on ciliate dynamics, suggesting that sampling at multiple depths in CW is not necessary to adequately monitor ciliate communities. Overall, our results suggest that macrophytes, location, and date of sampling influenced ciliated dynamics but stress the need for direct manipulative experiments of ciliate abundance, diversity, and composition conducted on a full annual cycle to better understand the impact of ciliates on nutrient cycling in CWs. This is especially true to determine if the associations found in our principal component
analysis are robust.
Fortuny, M.; Gamisans, X.; Deshusses, M.A.; Lafuente Sancho, Francisco Javier; Casas, C.; Gabriel, D. Water research (Oxford) Vol. 45, num. 17, p. 5665-5674 DOI: 10.1016/j.watres.2011.08.029 Data de publicació: 2011-11-01 Article en revista
Sludge treatment wetlands (STW) emerge as a promising sustainable technology with low energy requirements and operational costs. In this study, technical, economic and environmental aspects of STW are investigated and compared with other alternatives for sludge management in small communities (<2000 population equivalent). The performance of full-scale STW was characterised during 2 years. Sludge dewatering increased total solids (TS) concentration by 25%, while sludge biodegradation lead to volatile solids around 45% TS and DRI24h between 1.1 and 1.4 gO2/kgTS h, suggesting a partial stabilisation of biosolids. In the economic and environmental assessment, four scenarios were considered for comparison: 1) STW with direct land application of biosolids, 2) STW with compost post-treatment, 3) centrifuge with compost post-treatment and 4) sludge transport to an intensive wastewater treatment plant. According to the results, STW with direct land application is the most cost-effective scenario, which is also characterised by the lowest environmental impact. The life cycle assessment highlights that global warming is a significant impact category in all scenarios, which is attributed to fossil fuel and electricity consumption; while greenhouse gas emissions from STW are insignificant. As a conclusion, STW are the most appropriate alternative for decentralised sludge management in small communities.
Sludge treatment wetlands (STW) emerge as a promising sustainable technology with low
energy requirements and operational costs. In this study, technical, economic and environmental aspects of STW are investigated and compared with other alternatives for sludge management in small communities (<2000 population equivalent). The performance of fullscale STW was characterised during 2 years. Sludge dewatering increased total solids (TS)
concentration by 25%, while sludge biodegradation lead to volatile solids around 45% TS and DRI24h between 1.1 and 1.4 gO2/kgTS h, suggesting a partial stabilisation of biosolids. In the economic and environmental assessment, four scenarios were considered for comparison: 1) STW with direct land application of biosolids, 2) STW with compost post-treatment, 3) centrifuge with compost post-treatment and 4) sludge transport to an intensive wastewater
treatment plant. According to the results, STW with direct land application is the most
cost-effective scenario, which is also characterised by the lowest environmental impact. The life cycle assessment highlights that global warming is a significant impact category in all scenarios, which is attributed to fossil fuel and electricity consumption; while greenhouse gas emissions from STW are insignificant. As a conclusion, STW are the most appropriate alternative for decentralised sludge management in small communities.
5th. IWA International Young Water Professional 2010, qua atorga la International Water association
The oxygen transfer rate (OTR) has a significant impact on the design, optimal operation and modelling of constructed wetlands treating wastewater. Oxygen consumption is very fast in wetlands and the OTR cannot be determined using an oxygen mass balance. This problem is circumvented in this study by applying the gas tracer method. Experiments were conducted in an unplanted gravel bed (dimensions L × W × d 125 × 50 × 35 cm filled with a 30-cm layer of 10–11-mm gravel) and a planted horizontal subsurface flow constructed wetland (HSSFCW) (L × W × d 110 × 70 × 38 cm filled with a 30-cm layer of 3.5-mm gravel with Phragmites australis). Tap water saturated with propane as gas tracer (pure or commercial cooking gas, depending on the test) was used. The mass transfer ratio between oxygen and commercial propane gas was quite constant and averaged R = 1.03, which is slightly lower than the value of R = 1.39 that is usually reported for pure propane. The OTR ranged from 0.31 to 5.04 g O2 m−2 d−1 in the unplanted gravel bed and from 0.3 to 3.2 g O2 m−2 d−1 in the HSSFCW, depending on the hydraulic retention time (HRT). The results of this study suggest that the OTR in HSSFCW is very low for the oxygen demand of standard wastewater and the OTR calculations based on mass balances and theoretical stoichiometric considerations overestimate OTR values by a factor that ranges from 10 to 100. The gas tracer method is a promising tool for determining OTR in constructed wetlands, with commercial gas proving to be a viable low-cost alternative for determining OTR.
Monje, P.; González, S.; Moldes, D.; Vidal, T.; Moreira, M.; Feijoo, G. Water research (Oxford) Vol. 44, num. 7, p. 2211-2220 DOI: 10.1016/j.watres.2009.12.047 Data de publicació: 2010-04 Article en revista
Pérez-Moya, M.; Graells, M.; Castells, G.; Amigó, J.; Ortega, E.; Buhigas, G.; Martín, L.; Mansilla, H. Water research (Oxford) Vol. 44, num. 8, p. 2533-2540 DOI: 10.1016/j.watres.2010.01.032 Data de publicació: 2010-04 Article en revista
Baquerizo, G.; Maestre, J.; Machado, V.; Gamisans, X.; Gabriel, D. Water research (Oxford) Vol. 43, num. 8, p. 2293-2301 DOI: 10.1016/j.watres.2009.02.031 Data de publicació: 2009-05 Article en revista
Costán-Longaresa, A.; Montemayora, M.; Andrey, P.; Javier, M.; Jofre, J.; Mujeriego, R.; Francisco, L. Water research (Oxford) Vol. 42, num. 17, p. 4439-4448 Data de publicació: 2008-11 Article en revista
In conventional single-stage anaerobic digestion processes, hydrolysis is regarded as the rate-limiting step in the degradation of complex organic compounds, such as sewage sludge. Two-stage systems have been proposed to enhance this process. However, so far it is not clear which are the best conditions for a two-stage anaerobic digestion process of sewage sludge, in terms of temperature and hydraulic retention time of each stage. The aim of this work was to determine the optimal conditions for the hydrolytic–acidogenic stage treating real sludge with a high concentration of total solids (40–50 g L-1) and volatile solids (25–30 g L-1), named high concentration sludge. The variables considered for this first stage were: hydraulic retention time (1–4 days) and temperature (55 and 65 °C). Maximum volatile fatty acids generation was obtained at 4 days and 3 days hydraulic retention time for 55 °C and 65 °C, respectively. Consequently, 4 days hydraulic retention time and temperature of 55 °C were set as the working conditions for the hydrolytic–acidogenic stage treating high concentration sludge. The results obtained when operating with high concentration sludge were compared with a low concentration sludge consisting of 17–28 g L-1 total solids and 13–21 g L-1 volatile solids. The effect of decreasing the influent sludge pH, when working at the optimal conditions established, was also evaluated.
Impregnated resins prepared by the immobilization of an ionic liquid (IL, Cyphos IL-101, tetradecyl(trihexyl)phosphonium chloride) into a composite biopolymer matrix (made of gelatin and alginate) have been tested for recovery of Bi(III) from acidic solutions. The concentration of HCl slightly influenced Bi(III) sorption capacity. Bismuth(III) sorption capacity increased with IL content in the resin but non-linearly. Maximum sorption capacity reached 110-130mgBig(-1) in 1M HCl solutions. The mechanism involved in Bi recovery was probably an ion exchange mechanism, though it was not possible to establish the stoichiometric exchange ratio between BiCl(4)(-) and IL. Sorption kinetics were investigated through the evaluation of a series of parameters: metal concentration, sorbent dosage, type and size of sorbent particles and agitation speed. In order to reinforce the stability of the resin particles, the IL-encapsulated gels were dried; this may cause a reduction in the porosity of the resin particle and then diffusion limitations. The intraparticle diffusion coefficients were evaluated using the Crank's equation. Additionally, the pseudo-first-order and pseudo-second-order equations were systematically tested on sorption kinetics. Metal can be desorbed from loaded resins using either citric acid or KI/HCl solutions. The sorbent could be recycled for at least three sorption/desorption cycles.
Escalas-Cañellas, A.; Ábrego-Góngora, Carlos J.; Barajas-López, M.G.; Houweling, D.; Comeau, Y. Water research (Oxford) Vol. 42, num. 10-11, p. 2551-2562 DOI: 10.1016/j.watres.2008.02.016 Data de publicació: 2008-05 Article en revista
Thirty-nine linear regression and time series models were built and calibrated for influent temperature (Ti) estimation at the primary aerated facultative lagoon in a municipal wastewater treatment plant. The models were based on mean daily ambient air temperature (Ta) and/or daily rainfall (P), and—optionally—wastewater temperature autoregression. The best fits were achieved with some time series models involving Ta and P, and Ti autoregression. The best-fit model was able to estimate influent temperature with a root-mean-square-error of 0.5 °C, and an R2 of 0.925, for the calibration period of 10.5 months. In addition, a dynamic lagoon-temperature (Tw) model from the literature was modified in its terms of solar radiation and aeration latent heat, and applied to the primary lagoon. The model was fed with the estimated influent temperature, and five model parameters were identified by calibration against 10.5-month Tw data. Dynamic lagoon-temperature estimation results were comparable to or better than other results of long-term simulations found in the literature. Sensitivity analyses were run on both models. Further validation with independent sets of data is needed for verification of the predictive capability of the models.
Faced with the need to improve ammonia removal from lagoon wastewater treatment plants (WWTPs) operated in Quebec, Canada, mechanistic modelling has been proposed as a tool for explaining the seasonal nitrification phenomenon and to evaluate optimization and upgrade scenarios. A lagoon model that includes a modified activated sludge biokinetic model and that assumes completely mixed conditions in the water column and sediments has been applied to simulate 3 years of consecutive effluent data for a lagoon from the Drummondville WWTP. Successful prediction of results from this plant indicates that the seasonal nitrification is determined by temperature, dissolved oxygen (DO) concentrations, hydraulic retention time (HRT) of the water column and washout driven by a well-mixed water column. Results also indicate that sediments contribute to the ammonia load in the lagoon effluent, particularly in spring and early summer. Sensitivity analyses performed with the model indicate that the nitrification period could be prolonged by increasing DO concentrations in the lagoon and that bioaugmentation would be particularly effective in spring and early summer. Limitations of the model are discussed, as well as ways to improve the hydraulic model.
Otero, N.; Tolosana-Delgado, R.; Soler, A.; Pawlowsky, V.; Canals, A. Water research (Oxford) Vol. 39, num. 7, p. 1404-1414 DOI: 10.1016/j.watres.2005.01.012 Data de publicació: 2005-03-10 Article en revista