Nanofiltration and reverse osmosis for defluoridation: The role of inorganic carbon

Fluoride (F) concentrations above the World Health Organization (WHO) guideline value of 1.5 mg/L in drinking water can lead to serious health problems such as dental fluorosis and skeletal fluorosis. High F levels are often associated with carbonaceous (i.e. high inorganic carbon (IC)) type waters. The high fluoride concentrations in natural waters often occur in arid regions where no sufficient quantity of alternative water is readily available due to scarcity of water, consequently, treatment is the best option to provide safe drinking water. Nanofiltration (NF) and reverse osmosis (RO) are promising and appropriate membrane technologies for defluoridation due to their high fluoride removal efficiency and their ability to simultaneously remove a wide range of other inorganic and organic contaminants 1. Different ions can have various effects on F removal by NF/RO 2. IC in natural waters is present as carbonate ion (CO32-), bicarbonate ion (HCO3-), carbonic acid (H2CO3), and carbon dioxide (CO2) depending on the pH. Due to the different characteristics of these species it is important to study the impact of IC on F retention mechanisms at different pH. In this study the mechanisms of IC species impact on F retention by NF/RO has been investigated as a function of pH.Two commercial NF and RO membranes, BW30 and NF270 respectively from DOW Chemicals (USA) were used. Synthetic waters were prepared using realistic ranges of F and IC for carbonaceous waters found for example in the fluoride rich waters in Tanzania. Feed concentration of F and IC were 50 mgF/L as NaF and 500 mgC/L as NaHCO3 respectively. Visual MINTEQ software was used to predict the speciation of IC and F at various pH. Figure 1 indicates that the permeate F concentrations were high (35-47 mg/L) at pH 2 where F existed mainly as uncharged HF. At pH 8 and 11, when there was a change in speciation to F ion and the membranes were negatively charged, permeate F concentrations decreased drastically. Permeate F concentrations for the RO BW30 membrane were lower than that of the relatively open NF270. BW30 removed fluoride to meet WHO guideline value of 1.5 mg/L at pH 11 up to about 40% recovery, while NF270 did not achieve the guideline value at any pH studied. In the past, BW30 had achieved the guideline value at pH 8 but with relatively low electrical conductivity (EC) of about 2000 µS/cm. However, in the current study the high IC concentration resulted in high EC (3600 µS/cm) and high osmotic pressure. This led to a decrease in the net driving pressure thus facilitating the diffusion of F through the membrane 3. The predominant IC species at pH 2 was H2CO3. This resulted in very low feed IC concentrations (1-5 mg C/L, less than intended 500 mgC/L) at pH 2 due to degassing (H2CO3 decomposes to CO2). Monovalent HCO3- predominated at pH 8 and easily permeated the NF270 membrane. At pH 11, MINTEQ predicted divalent CO32- as the predominant IC species and permeate IC was lower than at pH 8 for the NF270. For the BW30 membrane, IC concentrations in the permeates were lower than the NF270 and impact of IC speciation was not observed. This suggests that the main retention mechanism of IC by the NF270 is charged repulsion and that of the RO BW30 membrane is size exclusion. Please click Additional Files below to see the full abstract

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Systems for ammonium concentration for further removal in the partial nitritation/anammox technology.

Anammox is one of the main processes discovered quite recently for removal of ammonium from wastewater. Anammox process is cost effective, in that low energy and carbon source is needed. Partial nitritation is a perquisite for anammox in wastewater treatment for removal nitrogen and therefore partial nitritation/Anammox technology is studied substantially and applied in full-scale. However, the technology at present can only be used to treat high rich ammonium streams. Application of Anammox for treatment of low ammonium wastewater is not possible because of low yield of Anammox bacteria. The study aimed at devising strategies for using the Anammox technology to treat wastewater streams with low concentration of ammonium nitrogen. The objective was to get systems that could concentrate ammonium from low ammonium waste streams, so as to be able to treat it with partial nitritation/Anammox process. Two methods were used to concentrate ammonium: ion exchange and reverse osmosis. Ion exchange method was used to concentrate UASB effluents of about 24 - 40 mg NH4-N/l to 188 - 367 mg  NH4-N/l respectively which is about 9 times the initial concentrations. At VRF 5, 163 mg  NH4-N/l concentrate was attained from 41.8 mg  NH4-N/l RO feed. Results also showed that concentrates from both methods are able to be treated with partial nitritation/Anammox technology. However it took more than 32 hours to complete treatment of ion exchange concentrates while it took less than 24 hours to finish the partial nitritation/Anammox process of RO concentrates. The longer time taken can be attributed to high salinity of the concentrates which is as a result of NaCl which was used for regeneration in ion exchange process. Both ion exchange and reverse osmosis are viable methods for concentrating ammonium from UASB effluents. Dissolved oxygen was very important factor that influenced the biological process

Bio-based recovery of organic carbon from municipal waste streams : Process optimization and microbial community dynamics

Resource recovery from waste contributes to the transition to a sustainable society. Municipal organic wastes have enormous potential for resource recovery due to the inherent organic content which makes it possible to obtain bio-based chemicals and bioenergy. In view of this, the focus of the current study was on the bio-based recovery of carbon from municipal organic wastes by exploring process optimization and microbial community dynamics of existing and new technologies for the recovery of bio-based products. The study involved two parts: 1) biogas production through direct anaerobic granule-based treatment of mainstream municipal wastewater; and 2) production of bio-based platform chemicals in the form of volatile fatty acids (VFAs) from sewage sludge and other municipal organic wastes through mixed microbiome co-fermentation. This Ph.D. project demonstrated a waste-to-value approach to shifting wastewater treatment plants to biorefineries for recovering valuable carbon resources through both direct anaerobic treatment of municipal wastewater and co-fermentation of municipal organic waste. The application of VFAs for other processes could lead to a bio-based production platform as an alternative to fossil-based processes.Resursåtervinning från avfall bidrar till omställningen till ett hållbart samhälle. Kommunalt organiskt avfall har en enorm potential för resursåtervinning på grund av det inneboende organiska innehållet som gör det möjligt att få fram biobaserade kemikalier och bioenergi. Med tanke på detta låg fokus för den aktuella studien på biobaserad återvinning av kol från kommunalt organiskt avfall genom att utforska processoptimering och dynamik hos mikrobiella samhällen hos befintliga och nya teknologier för återvinning av biobaserade produkter. Studien omfattade två delar: 1) biogasproduktion genom direkt anaerob granulatbaserad rening av kommunalt avloppsvatten; och 2) produktion av nya plattformskemikalier i form av flyktiga fettsyror (VFA) från avloppsslam och annat kommunalt organiskt avfall genom samfermentering av blandad mikrobiom. Detta Ph.D. projekt visade på ett avfall till värde synsätt på att förvandla avloppsreningsverk till bioraffinaderier för att återvinna värdefulla kolresurser genom både direkt anaerob behandling av kommunalt avloppsvatten och samjäsning med kommunalt organiskt avfall. Tillämpningen av VFA för andra processer skulle kunna leda till en biobaserad produktionsplattform som ett alternativ till fossilbaserade processer.QC 2022-03-09</p

Bio-based recovery of organic carbon from municipal waste streams : Process optimization and microbial community dynamics

Resource recovery from waste contributes to the transition to a sustainable society. Municipal organic wastes have enormous potential for resource recovery due to the inherent organic content which makes it possible to obtain bio-based chemicals and bioenergy. In view of this, the focus of the current study was on the bio-based recovery of carbon from municipal organic wastes by exploring process optimization and microbial community dynamics of existing and new technologies for the recovery of bio-based products. The study involved two parts: 1) biogas production through direct anaerobic granule-based treatment of mainstream municipal wastewater; and 2) production of bio-based platform chemicals in the form of volatile fatty acids (VFAs) from sewage sludge and other municipal organic wastes through mixed microbiome co-fermentation. This Ph.D. project demonstrated a waste-to-value approach to shifting wastewater treatment plants to biorefineries for recovering valuable carbon resources through both direct anaerobic treatment of municipal wastewater and co-fermentation of municipal organic waste. The application of VFAs for other processes could lead to a bio-based production platform as an alternative to fossil-based processes.Resursåtervinning från avfall bidrar till omställningen till ett hållbart samhälle. Kommunalt organiskt avfall har en enorm potential för resursåtervinning på grund av det inneboende organiska innehållet som gör det möjligt att få fram biobaserade kemikalier och bioenergi. Med tanke på detta låg fokus för den aktuella studien på biobaserad återvinning av kol från kommunalt organiskt avfall genom att utforska processoptimering och dynamik hos mikrobiella samhällen hos befintliga och nya teknologier för återvinning av biobaserade produkter. Studien omfattade två delar: 1) biogasproduktion genom direkt anaerob granulatbaserad rening av kommunalt avloppsvatten; och 2) produktion av nya plattformskemikalier i form av flyktiga fettsyror (VFA) från avloppsslam och annat kommunalt organiskt avfall genom samfermentering av blandad mikrobiom. Detta Ph.D. projekt visade på ett avfall till värde synsätt på att förvandla avloppsreningsverk till bioraffinaderier för att återvinna värdefulla kolresurser genom både direkt anaerob behandling av kommunalt avloppsvatten och samjäsning med kommunalt organiskt avfall. Tillämpningen av VFA för andra processer skulle kunna leda till en biobaserad produktionsplattform som ett alternativ till fossilbaserade processer.QC 2022-03-09</p

Recovery of organic carbon from municipal waste streams

The focus of the current study was on the recovery of carbon from municipal bio-waste streams. Firstly, the relationship between methanogenic pathways and the properties of anaerobic granules was studied using two pilot-scale upflow anaerobic sludge blanket (UASB) reactors with different granule size distribution. UASB1 granules were larger (3-4 mm) with multi-layered internal structure and the archaeal community was dominated by acetoclastic methanogens, while the UASB2 granules were smaller (1-2 mm) without a layered internal structure and the archaeal community was predominated by hydrogenotrophic methanogens. The acetoclastic methanogenic activities of UASB1 (250-437 mL CH4/g VS·d) than UASB2 (150-260 mL CH4/g VS·d), confirming that acetoclastic methanogenesis was more dominant in UASB1. Temperature increase from 20oC to 28oC did not change the microbial community but resulted in increased and stable biogas production for both reactors. There was an increase in chemical oxygen demand (COD) with hydraulic retention time due to increased contact time. The second part of the study focused on anaerobic co-digestion to produce volatile fatty acid (VFA) due to its higher value. The impact of substrate ratio of primary sludge (PS) and external organic waste (OW) and the robustness of the VFA system in the long term were assessed. Lab-scale batch study with different proportions of PS and OW; 0%, 25%, 50%, 75%, 100% of OW in terms of COD and scaled up in a semi-continuous pilot reactor with substrate ratio of 50% OW based on the results of the lab-scale study were performed. There was an increase in VFA production with an increase in OW proportion due to the availability of biodegradable organics. Acetic acid was the most dominant VFA in the batch reactors while in the semi-continuous experiment, caproic acid was dominated (50%). As carbon sources, the VFA-rich liquid attained the highest specific denitrification rate when compared with acetate and methanol.I kommunala avfallsströmmar finns det en stor potential för resursåtervinning på grund av det höga organiska innehållet vilket kan användas för biobaserade produkter. På grundval av detta så fokuserar denna studie på resursåtervinningen av kol från kommunala avfallsströmmar genom att undersöka nuvarande och nytillkomna tekniker för att få vattenreningssystem att också bli resursåtervinningssystem. Första delen av studien undersöker relationen mellan metanproduktion och karaktäriseringen av anaerobiska granuler med ändamålet att förbättra energiproduktionen genom direkt behandling av kommunalt avloppsvatten. För detta ändamål så användes två UASB (Upflow Anaerobic Sludge Blanket) pilotreaktorer. Reaktorerna kördes med olika stora granuler, olika temperaturinställningar och olika hydrauliska uppehållstider (HRTs). Storlek, mikrobiell struktur, intern mikrostruktur och specifik metanogenaktivitet av de anaerobiska granulerna analyserades. Granulerna i UASB1 var 3-4 mm stora med interna multilager av mikrostrukturer som bestod av acetoklastika-metanogen arkéer. Granulerna i UASB2 var 1- 2 mm stora utan interna multilager och bestod av hydrogenotrofa metanogener. Aktiviteten i granulerna i UASB1 var 250-437 mL CH4 /g VS·d och i UASB2 var det 150-260 mL CH4 /g VS·d, vilket bekräftar att de acetoklastisk-metanogesa var mer effektiva i UASB1 än de hydrogenotrofa i UASB2. Att öka temperaturen från 20 o C till 28 o C under försöket medförde ingen förändring av den mikrobiologiska strukturen, men gav en ökning i biogasproduktion i UASB1 och högre och stabilare biogasproduktionshastighet i UASB2. Ökningen av biogasproduktion berodde på en reduktion i metans löslighet i utflödet och stabilare metanogenes. Ökning i HRT resulterade i större reduktion av organiskt material mätt som kemisk syreförbrukning (COD) och större biogasproduktion på grund av längre kontakttid mellan substrat och mikroorganismer. Den andra delen av studien fokuserar på att utveckla ett tillvägagångssätt att få en anaerob rötning att producera flyktiga fettsyror (VFA) istället för biogas. Studien fokuserar på effekten som kvoten mellan substraten primärslam och externt matavfall (OW) har och hur robust VFA-systemet skulle vara i stor skala på lång sikt. Olika kvoter av primärslam och matavfall testades i labbskala i batchstudier med 0 %, 25 %, 50 %, 75 % och 100 % COD OW. Baserat på resultaten från labbskala så kördes 50% COD OW i ett semi-kontinuerligt pilotförsök. Batch-testerna i labbskala visade att högre % COD OW, gav högre VFA produktion på grund av högre koncentration av organiskt material. Ättiksyra var den mest förekommande VFAn i batch-testerna medan kapronsyra var högst förekommande (50%) i det semi-kontinuerliga försöket. Denitrifikationsförsök visade att VFA-rik vätska från pilotskalareaktorerna gav den högsta specifika denitrifikationshastigheten i jämförelse med acetat och metanol. Resultaten visar att värdefulla kolkällor kan återvinnas från kommunalt avfall genom anaerob behandling av kommunalt avloppsvatten och samfermentering av primärslam och matavfall.QC 2020-06-15</p

Recovery of organic carbon from municipal waste streams

The focus of the current study was on the recovery of carbon from municipal bio-waste streams. Firstly, the relationship between methanogenic pathways and the properties of anaerobic granules was studied using two pilot-scale upflow anaerobic sludge blanket (UASB) reactors with different granule size distribution. UASB1 granules were larger (3-4 mm) with multi-layered internal structure and the archaeal community was dominated by acetoclastic methanogens, while the UASB2 granules were smaller (1-2 mm) without a layered internal structure and the archaeal community was predominated by hydrogenotrophic methanogens. The acetoclastic methanogenic activities of UASB1 (250-437 mL CH4/g VS·d) than UASB2 (150-260 mL CH4/g VS·d), confirming that acetoclastic methanogenesis was more dominant in UASB1. Temperature increase from 20oC to 28oC did not change the microbial community but resulted in increased and stable biogas production for both reactors. There was an increase in chemical oxygen demand (COD) with hydraulic retention time due to increased contact time. The second part of the study focused on anaerobic co-digestion to produce volatile fatty acid (VFA) due to its higher value. The impact of substrate ratio of primary sludge (PS) and external organic waste (OW) and the robustness of the VFA system in the long term were assessed. Lab-scale batch study with different proportions of PS and OW; 0%, 25%, 50%, 75%, 100% of OW in terms of COD and scaled up in a semi-continuous pilot reactor with substrate ratio of 50% OW based on the results of the lab-scale study were performed. There was an increase in VFA production with an increase in OW proportion due to the availability of biodegradable organics. Acetic acid was the most dominant VFA in the batch reactors while in the semi-continuous experiment, caproic acid was dominated (50%). As carbon sources, the VFA-rich liquid attained the highest specific denitrification rate when compared with acetate and methanol.I kommunala avfallsströmmar finns det en stor potential för resursåtervinning på grund av det höga organiska innehållet vilket kan användas för biobaserade produkter. På grundval av detta så fokuserar denna studie på resursåtervinningen av kol från kommunala avfallsströmmar genom att undersöka nuvarande och nytillkomna tekniker för att få vattenreningssystem att också bli resursåtervinningssystem. Första delen av studien undersöker relationen mellan metanproduktion och karaktäriseringen av anaerobiska granuler med ändamålet att förbättra energiproduktionen genom direkt behandling av kommunalt avloppsvatten. För detta ändamål så användes två UASB (Upflow Anaerobic Sludge Blanket) pilotreaktorer. Reaktorerna kördes med olika stora granuler, olika temperaturinställningar och olika hydrauliska uppehållstider (HRTs). Storlek, mikrobiell struktur, intern mikrostruktur och specifik metanogenaktivitet av de anaerobiska granulerna analyserades. Granulerna i UASB1 var 3-4 mm stora med interna multilager av mikrostrukturer som bestod av acetoklastika-metanogen arkéer. Granulerna i UASB2 var 1- 2 mm stora utan interna multilager och bestod av hydrogenotrofa metanogener. Aktiviteten i granulerna i UASB1 var 250-437 mL CH4 /g VS·d och i UASB2 var det 150-260 mL CH4 /g VS·d, vilket bekräftar att de acetoklastisk-metanogesa var mer effektiva i UASB1 än de hydrogenotrofa i UASB2. Att öka temperaturen från 20 o C till 28 o C under försöket medförde ingen förändring av den mikrobiologiska strukturen, men gav en ökning i biogasproduktion i UASB1 och högre och stabilare biogasproduktionshastighet i UASB2. Ökningen av biogasproduktion berodde på en reduktion i metans löslighet i utflödet och stabilare metanogenes. Ökning i HRT resulterade i större reduktion av organiskt material mätt som kemisk syreförbrukning (COD) och större biogasproduktion på grund av längre kontakttid mellan substrat och mikroorganismer. Den andra delen av studien fokuserar på att utveckla ett tillvägagångssätt att få en anaerob rötning att producera flyktiga fettsyror (VFA) istället för biogas. Studien fokuserar på effekten som kvoten mellan substraten primärslam och externt matavfall (OW) har och hur robust VFA-systemet skulle vara i stor skala på lång sikt. Olika kvoter av primärslam och matavfall testades i labbskala i batchstudier med 0 %, 25 %, 50 %, 75 % och 100 % COD OW. Baserat på resultaten från labbskala så kördes 50% COD OW i ett semi-kontinuerligt pilotförsök. Batch-testerna i labbskala visade att högre % COD OW, gav högre VFA produktion på grund av högre koncentration av organiskt material. Ättiksyra var den mest förekommande VFAn i batch-testerna medan kapronsyra var högst förekommande (50%) i det semi-kontinuerliga försöket. Denitrifikationsförsök visade att VFA-rik vätska från pilotskalareaktorerna gav den högsta specifika denitrifikationshastigheten i jämförelse med acetat och metanol. Resultaten visar att värdefulla kolkällor kan återvinnas från kommunalt avfall genom anaerob behandling av kommunalt avloppsvatten och samfermentering av primärslam och matavfall.QC 2020-06-15</p

Recovery of organic carbon from municipal waste streams

The focus of the current study was on the recovery of carbon from municipal bio-waste streams. Firstly, the relationship between methanogenic pathways and the properties of anaerobic granules was studied using two pilot-scale upflow anaerobic sludge blanket (UASB) reactors with different granule size distribution. UASB1 granules were larger (3-4 mm) with multi-layered internal structure and the archaeal community was dominated by acetoclastic methanogens, while the UASB2 granules were smaller (1-2 mm) without a layered internal structure and the archaeal community was predominated by hydrogenotrophic methanogens. The acetoclastic methanogenic activities of UASB1 (250-437 mL CH4/g VS·d) than UASB2 (150-260 mL CH4/g VS·d), confirming that acetoclastic methanogenesis was more dominant in UASB1. Temperature increase from 20oC to 28oC did not change the microbial community but resulted in increased and stable biogas production for both reactors. There was an increase in chemical oxygen demand (COD) with hydraulic retention time due to increased contact time. The second part of the study focused on anaerobic co-digestion to produce volatile fatty acid (VFA) due to its higher value. The impact of substrate ratio of primary sludge (PS) and external organic waste (OW) and the robustness of the VFA system in the long term were assessed. Lab-scale batch study with different proportions of PS and OW; 0%, 25%, 50%, 75%, 100% of OW in terms of COD and scaled up in a semi-continuous pilot reactor with substrate ratio of 50% OW based on the results of the lab-scale study were performed. There was an increase in VFA production with an increase in OW proportion due to the availability of biodegradable organics. Acetic acid was the most dominant VFA in the batch reactors while in the semi-continuous experiment, caproic acid was dominated (50%). As carbon sources, the VFA-rich liquid attained the highest specific denitrification rate when compared with acetate and methanol.I kommunala avfallsströmmar finns det en stor potential för resursåtervinning på grund av det höga organiska innehållet vilket kan användas för biobaserade produkter. På grundval av detta så fokuserar denna studie på resursåtervinningen av kol från kommunala avfallsströmmar genom att undersöka nuvarande och nytillkomna tekniker för att få vattenreningssystem att också bli resursåtervinningssystem. Första delen av studien undersöker relationen mellan metanproduktion och karaktäriseringen av anaerobiska granuler med ändamålet att förbättra energiproduktionen genom direkt behandling av kommunalt avloppsvatten. För detta ändamål så användes två UASB (Upflow Anaerobic Sludge Blanket) pilotreaktorer. Reaktorerna kördes med olika stora granuler, olika temperaturinställningar och olika hydrauliska uppehållstider (HRTs). Storlek, mikrobiell struktur, intern mikrostruktur och specifik metanogenaktivitet av de anaerobiska granulerna analyserades. Granulerna i UASB1 var 3-4 mm stora med interna multilager av mikrostrukturer som bestod av acetoklastika-metanogen arkéer. Granulerna i UASB2 var 1- 2 mm stora utan interna multilager och bestod av hydrogenotrofa metanogener. Aktiviteten i granulerna i UASB1 var 250-437 mL CH4 /g VS·d och i UASB2 var det 150-260 mL CH4 /g VS·d, vilket bekräftar att de acetoklastisk-metanogesa var mer effektiva i UASB1 än de hydrogenotrofa i UASB2. Att öka temperaturen från 20 o C till 28 o C under försöket medförde ingen förändring av den mikrobiologiska strukturen, men gav en ökning i biogasproduktion i UASB1 och högre och stabilare biogasproduktionshastighet i UASB2. Ökningen av biogasproduktion berodde på en reduktion i metans löslighet i utflödet och stabilare metanogenes. Ökning i HRT resulterade i större reduktion av organiskt material mätt som kemisk syreförbrukning (COD) och större biogasproduktion på grund av längre kontakttid mellan substrat och mikroorganismer. Den andra delen av studien fokuserar på att utveckla ett tillvägagångssätt att få en anaerob rötning att producera flyktiga fettsyror (VFA) istället för biogas. Studien fokuserar på effekten som kvoten mellan substraten primärslam och externt matavfall (OW) har och hur robust VFA-systemet skulle vara i stor skala på lång sikt. Olika kvoter av primärslam och matavfall testades i labbskala i batchstudier med 0 %, 25 %, 50 %, 75 % och 100 % COD OW. Baserat på resultaten från labbskala så kördes 50% COD OW i ett semi-kontinuerligt pilotförsök. Batch-testerna i labbskala visade att högre % COD OW, gav högre VFA produktion på grund av högre koncentration av organiskt material. Ättiksyra var den mest förekommande VFAn i batch-testerna medan kapronsyra var högst förekommande (50%) i det semi-kontinuerliga försöket. Denitrifikationsförsök visade att VFA-rik vätska från pilotskalareaktorerna gav den högsta specifika denitrifikationshastigheten i jämförelse med acetat och metanol. Resultaten visar att värdefulla kolkällor kan återvinnas från kommunalt avfall genom anaerob behandling av kommunalt avloppsvatten och samfermentering av primärslam och matavfall.QC 2020-06-15</p

Production of volatile fatty acids through co-digestion of sewage sludge and external organic waste : Effect of substrate proportions and long-term operation

Volatile fatty acids (VFAs) are intermediates of anaerobic digestion with high value and wide range ofusage. Co-digestion of sewage sludge and external organic waste (OW) for VFA production can helpachieve both resource recovery and ensure sustainable and innovative waste management. In view ofthis, the effect of substrate proportions on VFA production from co-digestion of primary sewage sludgeand OW is studied. Long-term operation in a semi-continuous reactor was performed to assess the resilienceof such a system and the VFA-rich effluent was tested for its ability to be used as carbon source fordenitrification. Co-digestion was initially carried out in batch reactors with OW proportion of 0%, 25%,50%, 75%, 100% in terms of COD and scaled up in a semi-continuous reactor operation with 50% OW.In the short-term operation in the batch mode, acetic acid dominated, however, increasing OW fractionresulted in increased valeric and caproic acid production. Moreover, in the long-term semi-continuousoperation, caproic acid dominated, accounting for 55% of VFAs. The VFA-rich effluent from the semicontinuousreactor achieved the highest denitrification rate as a carbon source when compared withacetic acid and methanol. The results demonstrate that co-fermentation can increase VFA yield and shiftproducts from acetic acid to caproic acid in long-term operation and the VFAs can be used withinwastewater treatment plants to close the loop.QC 20200703</p