Grey water treatment at a sports centre for reuse in irrigation: a case study.

Grey water has long been considered a promising option for dealing with water scarcity and reuse. However, factors such as lack of macronutrients and low carbon content make its treatment challenging. The aim of this paper was to investigate the applicability of sequencing batch reactor (SBR) technology to on-site grey water treatment at a sports centre for reuse in irrigation. The results demonstrated that the regenerated water complied with microbiological parameters concerning restriction of solids and organic matter removal. Denitrification was not fully accomplished, but ammonium was totally oxidised and low concentrations of nitrates were achieved. Effluent with good appearance and no odour was used in an experimental study to irrigate a grid system containing natural and artificial grass sections. The conclusion is that SBR technology offers a promising treatment for grey water.

Boosting ethanol production rates from carbon dioxide in MES cells under optimal solventogenic conditions.

Microbial Electrosynthesis (MES) has been widely applied for acetic acid (HA) production from CO2 and electricity. Ethanol (EtOH) has a higher market value than HA, and wide application in industry and as a biofuel. However, it has only been obtained sporadically and at low concentrations, probably due to sub-optimal operating conditions. This study aimed at enhancing EtOH productivity in MES cells by jointly optimising key operation parameters, including pH, H2 and CO2 partial pressure (pH2 and pCO2), and HA concentration, to promote solventogenesis. Two H-type cells were operated in fed-batch mode at -0.8 V vs. SHE with CO2 as the sole carbon source. A mixed culture, enriched with Clostridium ljungdahlii was used as the biocatalyst. The combination of low pH (<4.5) and pCO2 (<0.3 atm), along with high HA concentration (about 6 g L-1) and pH2 (>3 atm), were mandatory conditions for maintaining an efficient solventogenic culture, dominated by Clostridium sp., capable of high-rate EtOH production. The maximum EtOH production rate was 10.95 g m-2 d-1, and a concentration of 5.28 g L-1 was achieved. Up to 30 % of the electrons and 15.2 % of the carbon provided were directed towards EtOH production, and 28.1 kWh were required for the synthesis of 1 kg of EtOH from CO2. These results highlight that strict conditions are required for a continuous, reliable, EtOH production in MES cells. Future investigation should focus on improving cell configuration to achieve EtOH production at higher current densities while minimizing the electric energy input.

CO2 in indoor environments: From environmental and health risk to potential renewable carbon source.

In the developed world, individuals spend most of their time indoors. Poor Indoor Air Quality (IAQ) has a wide range of effects on human health. The burden of disease associated with indoor air accounts for millions of premature deaths related to exposure to Indoor Air Pollutants (IAPs). Among them, CO2 is the most common one, and is commonly used as a metric of IAQ. Indoor CO2 concentrations can be significantly higher than outdoors due to human metabolism and activities. Even in presence of ventilation, controlling the CO2 concentration below the Indoor Air Guideline Values (IAGVs) is a challenge, and many indoor environments including schools, offices and transportation exceed the recommended value of 1000 ppmv. This is often accompanied by high concentration of other pollutants, including bio-effluents such as viruses, and the importance of mitigating the transmission of airborne diseases has been highlighted by the COVID-19 pandemic. On the other hand, the relatively high CO2 concentration of indoor environments presents a thermodynamic advantage for direct air capture (DAC) in comparison to atmospheric CO2 concentration. This review aims to describe the issues associated with poor IAQ, and to demonstrate the potential of indoor CO2 DAC to purify indoor air while generating a renewable carbon stream that can replace conventional carbon sources as a building block for chemical production, contributing to the circular economy.

Simultaneous domestic wastewater treatment and renewable energy production using microbial fuel cells (MFCs).

Microbial fuel cells (MFCS) can be used in wastewater treatment and to simultaneously produce electricity (renewable energy). MFC technology has already been applied successfully in lab-scale studies to treat domestic wastewater, focussing on organic matter removal and energy production. However, domestic wastewater also contains nitrogen that needs to be treated before being discharged. The goal of this paper is to assess simultaneous domestic wastewater treatment and energy production using an air-cathode MFC, paying special attention to nitrogen compound transformations. An air-cathode MFC was designed and run treating 1.39 L d(-1) of wastewater with an organic load rate of 7.2 kg COD m(-3) d(-1) (80% removal efficiency) and producing 1.42 W m(-3). In terms of nitrogen transformations, the study demonstrates that two different processes took place in the MFC: physical-chemical and biological. Nitrogen loss was observed increasing in line with the power produced. A low level of oxygen was present in the anodic compartment, and ammonium was oxidised to nitrite and nitrate.

Combining partial nitritation and heterotrophic denitritation for the treatment of landfill leachate previous to an anammox reactor.

Landfill leachate can present extremely elevated concentrations of ammonium (up to 6,000 mg N-NH(4) (+) L(-1)) and a low biodegradable organic matter fraction. As an alternative to conventional systems, this wastewater can be treated on a more sustainable way by a fully autotrophic partial nitritation-anammox system. The operation of the first step of this system, the partial nitritation, is critical since the elevated concentrations of ammonium and nitrite in the reactor can severely inhibit ammonium oxidizing bacteria (AOB) activity. In this way, the inclusion of anoxic phases during the feeding events to promote the denitrification via nitrite can be a good option for upgrading the process performance and increasing the stability of the system. This paper deals with the evaluation of an anoxic-aerobic step-feed strategy for the operation of a partial nitritation SBR. Results of this study have revealed a decrease on the total nitrogen inside the reactor of more than 200 mg N L(-1) without prejudice on the partial nitritation process. Furthermore, this study has also allowed detecting an AOB activity reduction at the end of aerobic phases due to bicarbonate limitation and/or free nitrous acid inhibition.

Systematic model development for partial nitrification of landfill leachate in a SBR.

This study deals with partial nitrification in a sequencing batch reactor (PN-SBR) treating raw urban landfill leachate. In order to enhance process insight (e.g. quantify interactions between aeration, CO(2) stripping, alkalinity, pH, nitrification kinetics), a mathematical model has been set up. Following a systematic procedure, the model was successfully constructed, calibrated and validated using data from short-term (one cycle) operation of the PN-SBR. The evaluation of the model revealed a good fit to the main physical-chemical measurements (ammonium, nitrite, nitrate and inorganic carbon), confirmed by statistical tests. Good model fits were also obtained for pH, despite a slight bias in pH prediction, probably caused by the high salinity of the leachate. Future work will be addressed to the model-based evaluation of the interaction of different factors (aeration, stripping, pH, inhibitions, among others) and their impact on the process performance.

The effect of urban landfill leachate characteristics on the coexistence of anammox bacteria and heterotrophic denitrifiers.

Heterotrophic denitrification coexists with the anammox process contributing to N removal owing to the biodegradable organic matter supply from urban landfill leachate and the decay of microorganisms. Both biomasses consumed nitrite increasing the nitrite requirements of the system. The aim of this paper is the study of the causes which induce the system to decrease nitrogen removal efficiency. In this study, urban landfill leachate has been treated in an anammox Sequencing Batch Reactor (SBR) for 360 days. The anammox reactor treated on average 0.24 kgN m(-3) d(-1) obtaining nitrogen removal efficiencies up to 89%. The results demonstrated that i) a suitable influent nitrite to ammonium molar ratio is a crucial factor to avoid troubles in the anammox reactor performance; ii) an excess of nitrite implied nitrite accumulation in the reactor; iii) a lower nitrite supply than the necessary for the system could force a loss of specific anammox activity due to nitrite competition with denitrifiers. These results pointed out the importance of the previous partial-nitritation process control in order to obtain a correct influent nitrite to ammonium molar ratio for the anammox reactor. In addition, sudden variation of the leachate characteristics must be avoided.

Effect of cycle changes on simultaneous biological nutrient removal in a sequencing batch reactor (SBR).

The destabilization of a microbial population is sometimes hard to solve when different biological reactions are coupled in the same reactor as in sequencing batch reactors (SBRs). This paper will try to guide through practical experiences the recovery of simultaneous nitrogen and phosphorus removal in an SBR after increasing the demand of wastewater treatment by taking advantage of its flexibility. The results demonstrate that the length of phases and the optimization of influent distribution are key factors in stabilizing the system for long-term periods with high nutrient removal (88%, 93% and 99% of carbon, nitrogen and phosphorus, respectively). In order to recover a biological nutrient removal (BNR) system, different interactions such as simultaneous nitrification and denitrification and also phosphorus removal must be taken into account. As a general conclusion, it can be stated there is no such thing as a perfect SBR operation, and that much will depend on the state of the BNR system. Hence, the SBR operating strategy must be based on a dynamic cycle definition in line with process efficiency.

Selection between alcohols and volatile fatty acids as external carbon sources for EBPR.

The purpose of this paper is to provide a basis for selecting alcohols (i.e. ethanol and methanol) or short-chain volatile fatty acids (VFAs) (i.e. acetate and propionate) as the external carbon sources for enhanced biological phosphorus removal (EBPR) from wastewaters in adapted or unadapted activated sludge. When ethanol is used in an unacclimated process, a period of adaptation is required by polyphosphate-accumulating organisms (PAOs). From 0 to 140 days of ethanol acclimatizing, the P release and uptake rates increased to 6.2 and 7.0 mgP-PO(3)4(-)g(-1)VSSh(-1), respectively. PAOs in ethanol-enriched sludge produced poly-beta-hydroxyvalerate (PHV) (81.9%) as the main polyhydroxyalkanoate (PHA) and reached an effluent phosphate concentration close to zero (0.10 mgP-PO(3)4(-)L(-1)). On the other hand, methanol was not used by PAOs in 30-day ethanol-acclimated sludge in short-term tests. If EBPR needs to be incidentally supported by substrate addition, VFAs are preferred; for long-term addition also ethanol can be considered.

Heterotrophic denitrification on granular anammox SBR treating urban landfill leachate.

The anammox process was applied to treat urban landfill leachate coming from a previous partial nitritation process. In presence of organic matter, the anammox process could coexist with heterotrophic denitrification. The goal of this study was to asses the stability of the anammox process with simultaneous heterotrophic denitrification treating urban landfill leachate. The results achieved demonstrated that the anammox process was not inactivated by heterotrophic denitrification. Moreover, part of the nitrate produced by anammox bacteria and part of the influent nitrite were removed by heterotrophic denitrifiers with associated biodegradable organic matter consumption. In this sense, the contribution on nitrogen removal of each process was calculated using a nitrogen mass balance methodology. An 85.1+/-5.6% of the nitrogen consumption was achieved via anammox process while the average heterotrophic denitrifiers contribution was 14.9+/-5.6%. Heterotrophic denitrification was limited by the available easily biodegradable organic matter.

Partial ammonium oxidation to nitrite of high ammonium content urban landfill leachates.

In an effort to treat N-rich streams in a more sustainable way, recent years have seen the development of new technologies, most of which are based on autotrophic denitrification via nitrite (anammox). In order to attain a suitable influent for that process, the wastewater must be treated by partially oxidising the ammonium to nitrite. In that aspect, this article presents the start-up and operation of a Partial Nitritation Sequencing Batch Reactor (PN-SBR) treating urban landfill leachates. Stable partial nitritation has been reached treating high ammonium loads (1-1.5 kg Nm(-3)d(-1)), demonstrating the feasibility of this technology as a previous step of anammox process. This study has also given away the importance of pH influence over ammonium oxidising bacteria (AOB) activity, thus it has been possible to determine the values of the half inhibition constants for free ammonia (k(I,FA)=605.48+/-87.18 mg N-NH L(-1)) and free nitrous acid (k(I,FNA)=0.49+/-0.09 mg N-HNO2 L(-1)), as well as the half-saturation constant for bicarbonate (k(HCO3-) = 0.01 +/- 0.16 mg CL(-1)).

Biological nutrient removal by applying SBR technology in small wastewater treatment plants: carbon source and C/N/P ratio effects.

SBR technology is considered an alternative to conventional processes such as Phoredox, Five-stage Bardenpho, among the others for treating nutrients in wastewaters. It is especially applicable to small communities of a just few people to a population equivalent (p.e) up to 4000. In this paper, biological nutrient removal using SBR technology in a single reactor is presented. Biological nutrient removal requires a sequence of anaerobic-anoxic-aerobic phases with multiple feeding events over one cycle. This filling strategy was adapted to enhance denitrification and phosphate release, using the easily biodegradable organic matter from the wastewater. In spite of using this feeding strategy, the organic matter concentration can be insufficient. The results show that biological nutrient removal was successfully achieved by using only one reactor, working with a low organic matter concentration in the influent (C/N/P ratio of 100:12:1.8). Nevertheless, when the C/P ratio was lower than 36 g COD x g(-1) P-P04, an accumulation of phosphate was observed. After that, the system responded quickly and returned to ideal conditions (C/P ratio of 67 g COD x g(-1) P-PO4), taking only 15 days to achieve the complete nutrient removal. Furthermore, the operational conditions and the synthetic wastewater used conferred a selective advantage to polyphosphate accumulating organisms (PAOs) over glycogen accumulating non-poly-P organisms (GAOs) as shown by the FISH analysis performed.

[Risk factors for the occurrence of sporadic Campylobacter, Salmonella and rotavirus diarrhea in preschool children]. / Factores de riesgo de los casos esporádicos de diarrea por Campylobacter, Salmonella y rotavirus en niños preescolares.

BACKGROUND: Sporadic cases of diarrhea in preschool children are highly frequent, especially those caused by rotavirus, Campylobacter and Salmonella. The aim of this study was to identify some of the factors associated with these processes. MATERIAL AND METHODS: A case-control study of hospitalized incident cases aged less than 3 years old was performed. Questionnaires were administered at admission, before the results of stool tests were known. Susceptibility, food exposure, and environmental factors were investigated. Infants aged less than 1 year were analyzed separately. RESULTS: A total of 117 patients (rotavirus in 31, Campylobacter in 228 and Salmonella in 21, negative results in 37) and 84 controls were studied. Several protective factors, such as breast feeding and prior antibiotic use, were identified. Risk factors for diarrhea were exposure to meat products (eating or environmental exposure in the kitchen), some kinds of pets, and attendance at day care. Differences were found by etiology and age. In the culture-negative group, no risk factors were identified. CONCLUSION: The problems posed by epidemiological study of this issue are discussed. The main findings in each group of cases are interpreted and proposals are made for their application in the control and prevention of these diseases.

An on-line optimisation of a SBR cycle for carbon and nitrogen removal based on on-line pH and Our: the role of dissolved oxygen control.

A pilot plant sequencing batch reactor (SBR) was applied in a wastewater treatment plant treating urban wastewater focused on carbon and nitrogen removal. From an initial predefined step-feed cycle definition, the evolution of the on-line monitored pH and calculated oxygen uptake rate (OUR) were analysed in terms of knowledge extraction. First, the aerobic phases of the SBR cycle were operated using an On/Off dissolved oxygen (DO) control strategy that concluded with a sinusoidal pH profile that made detecting the "ammonia valley" difficult. After changing to fuzzy logic control of the dissolved oxygen and by adding an air flow meter to the pilot plant, the pH evolution and on-line calculated OUR showed a clearer trend during the aerobic phases. Finally, a proposed algorithm for adjusting the aerobic phases of the SBR for carbon and ammonia removal is presented and discussed.

Evaluating the application of a decision support system in identifying adequate wastewater treatment for small communities. A case study: the Fluvia River Basin.

The identification of adequate wastewater treatment for small communities is a complex problem since it demands a combination of data from different sources, such as aspects of the community and landscape, the receiving environment and the available wastewater treatment technologies. The Catalan Water Agency (Agència Catalana de l'Aigua) considered using an EDSS (Environmental Decision Support System) as a tool to help water managers select the most adequate treatment for the urban wastewater of nearly 3,500 small communities in Catalonia (Spain). From that moment, EDSS was applied to all the river basins in Catalonia. In this paper the authors present the results obtained for the 76 small communities located in one of these river basins: the Fluvia River Basin. The characteristics of the community used in the reasoning process of the EDSS, the list of selected wastewater treatment alternatives, the technical environmental justification for the selected treatments and the reasons for discarding, favouring or disadvantaging them are presented. Finally, some results for the Fluvia River Basin are compared with those obtained in other Catalan river basins with different characteristics in order to evaluate which are the significant features in identifying adequate wastewater treatments.

Microbial electrosynthesis of butyrate from carbon dioxide.

This work proves for the first time the bioelectrochemical production of butyrate from CO2 as a sole carbon source. The highest concentration of butyrate achieved was 20.2 mMC, with a maximum butyrate production rate of 1.82 mMC d(-1). The electrochemical characterisation demonstrated that the CO2 reduction to butyrate was hydrogen driven. Production of ethanol and butanol was also observed opening up the potential for biofuel production.

Wastewater nitrogen removal in Sbrs, applying a step-feed strategy: from lab-scale to pilot-plant operation.

One of the problems of nitrogen removal from wastewater when applying sequencing batch reactor (SBR) technology, is the specific use of organic matter for denitrification purposes. Since easily biodegradable organic matter is rapidly consumed under aerobic or anoxic conditions (i.e. aerobic oxidation or anoxic denitrification, respectively), it is an important factor to consider when scaling up SBRs from the laboratory to real plant operation. In this paper, we present the results obtained in relation to scaling up reactors from lab-scale to pilot-plant scale, treating real wastewater from two different locations: the laboratory and in situ, respectively. In order to make using easily biodegradable organic matter more efficient, the filling phases of SBR cycles were adjusted according to a step-feed strategy composed of 6 anoxic-aerobic events. Feeding only occurred during anoxic phases. The results obtained demonstrated that the methodology may be useful in treating real wastewater with high carbon and nitrogen variations, as it always kept effluent levels lower than the official standards require (effluent total COD lower than 125 mg COD/L and effluent Total Nitrogen lower than 15 mg N/L).

Anoxic phases are the main N2O contributor in partial nitritation reactors treating high nitrogen loads with alternate aeration.

Partial nitritation (PN) reactors treating complex industrial wastewater can be operated by alternating anoxic-aerobic phases to promote heterotrophic denitrification via NO2(-). However, denitrification under stringent conditions can lead to high N2O production. In this study, the suitability of including anoxic phases in a PN-SBR treating real industrial wastewater was assessed in terms of process performance and N2O production. The PN-SBR was operated successfully and, when the HCO3(-):NH4(+) molar ratio was adjusted, produced a suitable effluent for a subsequent anammox reactor. 10-20% of the total influent nitrogen was removed. N2O production accounted for 3.6% of the NLR and took place mainly during the anoxic phases (60%). Specific denitrification batch tests demonstrated that, despite the availability of biodegradable COD, NO2(-) denitrification advanced at a faster rate than N2O denitrification, causing high N2O accumulation. Thus, the inclusion of anoxic phases should be avoided in PN reactors treating industrial wastewaters with high nitrogen loads.