Increased energy recovery and enhanced pathogen inactivation through anaerobic digestion of thickened wastewater sludge
Bibliographic record
Abstract
This study had two objectives: to investigate the possibility of increased energy recovery from anaerobic digestion of sewage sludge and to inactivate pathogens in wastewater sludge by means other than thermophilic temperature.All research was done through numerous lab experiments using wastewater sludge from the North End Water Pollution Control Centre in Winnipeg.It was proposed that toxicity from un-ionized form of VFA could be used in acid mesophilic (38"C) and low-mesophilic (24'C) conditions.The toxicity from the un- ionized form of VFA is based on cytoplasm acidification from a proton released after acid iontzation inside the bacterial cell and anion accumulation inside the cell which may lead to osmotic stress.Batch acid digesters were able to achieve Class A biosolids standards with respect to fecal coliforms concentrations under both operating conditions.When acid digesters were operated in semi-continuous mode, three acid digesters operated in series were needed to achieve Class A level.This was possible in mesophilic conditions only.Effluent from the three mesophilic acid digesters operated in series also showed highest inactivation of Ascaris suum ova from all systems tested, achieving complete inactivation of eggs enclosed in sentinels and2.8o/oviability of free floating eggs.Sludge thickening, which results in sludge flow reduction, was chosen as a method to achieve enhanced energy recovery.To establish optimum solids content in sludge, a series of hydrolysis tests were performed.The tests were to assess the impact of environmental conditions, such as operating temperature and sludge thickness on digestion.Optimum sludge solids content was defined as solids content that does not Abbreviations and Symbols ITPAD -l't digester (thermophilic) of two-phase digestion system 2TPAD -2nd digester (mesophilic) of two-phase digestion system ADanaerobic digestion AHABanaerobic hydrolytic-acidogenic bacteria C -concentration COD -chemical oxygen demand CODinr-influent chemical oxygen demand, mgCOD/l COD"¡¡effluent chemical oxygen demand, mgCOD/l D -diffusion coefficient Fconcentration of degradable particulate COD, mgCOD/l Fo -initial concentration of degradable particulate COD, mgCOD/l Gloss of COD attributed to biogas production, mgCOD/l J-flux fudecay coefficient, d-l K¡¡ -Henry's constant kr, -first-order hydrolysis rate constant, d-l K,saturation constant, mgll MADmesophilic anaerobic digestion MPNmost probable number pnet specific growth rate, d-l pmax -maximum specific growth rate, d-l Pacid phase products, mgCOD/l XVIII Pp -partial pressure PCOD"rn -particulate COD in effluent, mg COD/I PCOD;.¡-particulateCOD in influent, mg COD/I PS -Primary Sludge Q -flow, Vd or m3ld Psrudee -specific gravity of sludge, kgl^t SCODsoluble chemical oxygen demand SRTsolids retention time STPstandard conditions, OoC and I atmosphere pressure Ttemperature TADthermophilic anaerobic digestion T¿¡.-air temperature, oC TCODtotal chemical oxygen demandTdis"r,".-temperature in digester, oCTea.thearth temperature, oC Texchansercotd * temperature on the cold side of the heat exchanger, oC TexchanserHottemperature on the hot side of the heat exchanger, oC Tinco-ins studge -temperature of incoming sludge, oC TPADtemperature-phased anaerobic digestion TStotal solids U-VFAun-ionized form of VFA Vvolume VARvector atlraction reduction XlX VcH¿ -volume of methane produced, m3 CH¿ld VFAvolatile fatry acids VFA"6 -concentration of volatile fatty acids in effluent, mg COD/I VFAinrconcentration of volatile fatty acids in influent, mg COD/I VSvolatile solids VSin -influent mass of volatile solids, kg VS/d VSou, -effluent mass of volatile solids, kg VS/d VSRvolatile solids reduction, oZ WAS -Waste Activated Sludge Xncnconcentration of acidogenic population in digester, mgCOD/l Xcu+concentration of methanogenic population in digester, mgCOD/l Xdeclndecrease in concentration of acidogenic population in digester due to bacterial decay, mgCOD/l XdcH+decrease in concentration of methanogenic population in digester due to bacterial decay, mgCOD/l Xgecroincrease in concentration of acidogenic population in digester due to bacterial growth, mgCOD/l Xgcn+increase in concentration of methanogenic population in digester due to bacterial growth, mgCOD/l Xo -initial concentration of viable acidogenic population in raw sludge, mg COD/I Ytrue yield, mg biomass / mg COD Yob,observed yield, mg biomass / mg COD 4.1 Pathogeninactivation
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".