This work focuses on fermentation of pre-treated waste activated sludge (WAS) to generate volatile fatty acids (VFAs). Pre-treatment by high-pressure thermal hydrolysis (HPTH) was shown to aid WAS ...fermentation. Compared to fermentation of raw WAS, pre-treatment enabled a 2–5x increase in VFA yield (gVFACODgTCOD−1) and 4–6x increase in VFA production rate (gVFACODL−1d−1).
Three sludges, pre-treated in full-scale HPTH plants, were fermented. One was from a plant processing a mix of primary sludge and WAS and the other two from plants processing solely WAS. The HPTH plants solubilised suspended matter, evidenced by a 20–30% decrease in suspended solids and an increase of soluble COD : total COD from 0.04 to 0.4. Fermentation of the three sludges yielded similar VFA concentrations (15–20gVFACODL−1). The yields were largely independent of retention time (1d–6d) and temperature (42°C, 55°C). Also, the product spectrum depended mostly on the composition of the sludge rather than on operating conditions.
Poly(3-hydroxybutyrate) (PHB) was accumulated in full-scale municipal waste activated sludge at pilot scale. After accumulation, the fate of the PHB-rich biomass was evaluated over two weeks as a ...function of initial pH (5.5, 7.0 and 10), and incubation temperature (25, 37 and 55°C), with or without aeration. PHB became consumed under aerobic conditions as expected with first order rate constants in the range of 0.19 to 0.55 d−1. Under anaerobic conditions, up to 63 percent of the PHB became consumed within the first day (initial pH 7, 55°C). Subsequently, with continued anaerobic conditions, the polymer content remained stable in the biomass. Degradation rates were lower for acidic anaerobic incubation conditions at a lower temperature (25°C). Polymer thermal properties were measured in the dried PHB-rich biomass and for the polymer recovered by solvent extraction using dimethyl carbonate. PHB quality changes in dried biomass, indicated by differences in polymer melt enthalpy, correlated to differences in the extent of PHB extractability. Differences in the expressed PHB-in-biomass melt enthalpy that correlated to the polymer extractability suggested that yields of polymer recovery by extraction can be influenced by the state or quality of the polymer generated during downstream processing. Different post-accumulation process biomass management environments were found to influence the polymer quality and can also influence the extraction of non-polymer biomass. An acidic post-accumulation environment resulted in higher melt enthalpies in the biomass and, consequently, higher extraction efficiencies. Overall, acidic environmental conditions were found to be favourable for preserving both quantity and quality after PHB accumulation in activated sludge.
Display omitted
•Intracellular PHB depolymerase activity can be constrained anaerobically.•Changes in environmental conditions cause polymer loss even for short term storage.•Extracellular depolymerase activity is limited if PHB remains intracellular.•Acidic conditions are preferred to preserve quantity and quality for PHB recovery.•The melting properties of PHB in the biomass may influence the polymer extractability.
A pilot-scale process was operated over 22 months at the Brussels North Wastewater Treatment Plant (WWTP) in order to evaluate polyhydroxyalkanoate (PHA) production integration with services of ...municipal wastewater and sludge management. Activated sludge was produced with PHA accumulation potential (PAP) by applying feast-famine selection while treating the readily biodegradable COD from influent wastewater (average removals of 70% COD, 60% CODsol, 24% nitrogen, and 46% phosphorus). The biomass PAP was evaluated to be in excess of 0.4gPHA/gVSS. Batch fermentation of full-scale WWTP sludge at selected temperatures (35, 42 and 55 °C) produced centrate (6-9.4 gCODVFA/L) of consistent VFA composition, with optimal fermentation performance at 42 °C. Centrate was used to accumulate PHA up to 0.39 gPHA/gVSS. The centrate nutrients are a challenge to the accumulation process but producing a biomass with 0.5 gPHA/gVSS is considered to be realistically achievable within the typically available carbon flows at municipal waste management facilities.
Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with comparable properties to some petroleum-based polyolefins. PHA production can be achieved in open, mixed microbial cultures and thereby ...coupled to wastewater and solid residual treatment. In this context, waste organic matter is utilised as a carbon source in activated sludge biological treatment for biopolymer synthesis. Within the EU project Routes, the feasibility of PHA production has been evaluated in processes for sludge treatment and volatile fatty acid (VFA) production and municipal wastewater treatment. This PHA production process is being investigated in four units: (i) wastewater treatment with enrichment and production of a functional biomass sustaining PHA storage capacity, (ii) acidogenic fermentation of sludge for VFA production, (iii) PHA accumulation from VFA-rich streams, and (iv) PHA recovery and characterisation. Laboratory- and pilot-scale studies demonstrated the feasibility of municipal wastewater and solid waste treatment alongside production of PHA-rich biomass. The PHA storage capacity of biomass selected under feast-famine with municipal wastewater has been increased up to 34% (g PHA g VSS(-1)) in batch accumulations with acetate during 20 h. VFAs obtained from waste activated sludge fermentation were found to be a suitable feedstock for PHA production.
► Product inhibition restricts fermentation of pre-treated waste activated sludge. ► A threshold model (based on thermodynamics) best describes fermentation of THP-WAS. ► Threshold VFA concentration ...for THP-WAS fermentation is about 17gVFA(COD)/L. ► Product inhibition is due to a combination of VFAs (C2-C6). ► All VFAs except for acetate have the same impact; acetate is 50% as inhibitory.
Fermentation of waste activated sludge produces volatile fatty acids (VFAs), which can be used as the carbon sources for numerous biological processes. However, product inhibition can limit extent of fermentation to VFAs. In this study, product inhibition during fermentation of waste activated sludge pre-treated by a thermal hydrolysis process (THP-WAS) was investigated. Product inhibition was confirmed as spiking reactors with high levels of a mix of VFAs prevented fermentation taking place. Various inhibition models were trialled and it was found that a threshold model (based on thermodynamics) provided the best fit between model and data. This is the first time that threshold type inhibition has been shown for a mixed substrate, mixed population system. Batch fermentations carried out with THP-WAS of different dilutions were used to evaluate the impact of different organic loadings. The threshold VFA concentration for the systems studied was determined to be 17±1gCODVFAL−1. Inhibition was shown to be due to the presence of a combination of VFAs containing 2–6 carbon atoms each. When evaluated individually, by spiking individual VFAs, all VFAs except for acetate had the same impact at this threshold; acetate being approximately 50% as inhibitory as the other organic acids (COD basis). Based on this, a weighted model could be proposed to better represent the data. Strategies to improve overall yield could be increased production of acetate, or dilution to below the inhibitory level.
The purpose of this article is to highlight the growing need for small-scale, passive, natural systems that can serve our needs in water pollution control both in small communities and larger urban ...developments. Engineered wetlands represent one potential wastewater management option that exhibits promise in satisfying community requirements for contaminant and pathogen removal. However, the Canadian climate presents special challenges for constructed wetland treatment systems whose functional reliability is not nearly as well developed as currently available, more conventional, but less sustainable treatment options. The goal of this article is to present some of the key issues that require more fundamental understanding if engineered wetlands are to become a predictable, mainstream approach for decentralized wastewater treatment. Two critical factors limiting the advancement of treatment wetland technologies are a standardized approach to elucidate extant process mechanisms and a basis with which to make more meaningful comparisons within and between systems that naturally evolve and mature with time.
Recovery of
and
via struvite precipitation (SP) was evaluated from liquor of thermally pretreated waste activated sludge, containing high levels of nutrients (1500 mg
and 650 mg
), organics (45.5 g ...COD/L) and suspended solids (3.5 g TSS/L), with reference to anaerobically digested sludge centrate. In a series of jar tests, the order of pH adjustment and chemical addition were first tested for the digested sludge centrate. The effects of MgCl
2
and MgO, as Mg
2+
sources, on SP were evaluated in both waste streams. Up to 80% of the dissolved
was recovered using MgO (pH=9.2) from the pretreated sludge liquor and more than 86% of
from the digested sludge centrate (pH=8.0-8.5) regardless of the Mg
2+
source used.
recovery from digested sludge centrate required the addition of alkali, Mg
2+
source and
, making the process less viable. The precipitates contained mostly struvite and some levels of Ca
2+
, Fe
2+
and other Mg
2+
phosphates. The levels of solids, inorganics and organics in the waste streams influenced SP, specifically struvite crystal formation and settleability in the pretreated sludge liquor, which suggests that the applicability of SP for nutrient recovery from complex waste streams requires case-by-case testing, and process optimization.
A recent study showed that drought stress was the major factor causing yield loss of the sugar beet crop in the UK. That study has been extended here by modelling potential and rain-fed yields ...(1961–1995) for European areas where irrigation of sugar beet is uncommon. The inputs to this study are an improved crop growth model, the European monthly half-degree gridded meteorological data time series, and a map of soil texture and available water capacity in sugar beet growing regions. Model outputs were scaled using a ratio of national mean to experimental plot yields to reflect commercial performance of a hypothetical 1998 variety for all years. The model was run on daily weather data reconstructed from monthly values. Potential yields increased from north to south and from west to east due to increased radiation receipts. Drought losses were greatest in east Ukraine and southern Russia, at over 40% of potential yield (5
t
ha
−1). Losses were intermediate (15–30% or about 2
t
ha
−1) in central Ukraine, west Poland, east Germany and England (sandy soils) and lowest in NW Europe and west Ukraine. Increasing continentality decreases the number of rainy days per month during summer and the fraction of diffuse radiation; this reduces the radiation use efficiency by as much as 11%. Model output was also used to examine the efficiency of sugar beet production across Europe; at the extremes, NW European farmers deliver about 80% of the potential rain-fed yield while Polish farmers are only able to deliver 40%. This study demonstrates the importance of breeding for drought stress tolerance in Europe.
Patterns of microbial fatty acids (MFAs) from activated sludge samples were analyzed over one year's operation at the Hamilton Woodward municipal wastewater treatment plant in Canada. The objective ...was to examine community structure dynamics and to consider the potential for interrelationships between the population dynamics and treatment performance. With the exception of a higher than normal solids discharge on one day, the treatment plant operations were otherwise stable during the year. As such, wastewater temperature appeared to be the dominant influence on the observed dynamics of the MFA community structure. MFA monitoring and analysis was demonstrated as a practical diagnostic tool in community structure trend monitoring. While the findings did suggest potential for full-scale treatment process monitoring, further development is required. Advancement in technique and greater insight for the data interpretation will be made with historical data from continued case studies. In future studies, selective sub-sampling of biomass fractions (settling and dispersed fauna), evolution in the compositional analysis methods, and, ideally, complementary genotypic and classical microscopic analyses on select samples are recommended.
The objective of the present investigation has been to combine tracer principles and a hydrolytic microbial activity assay using fluorescein diacetate to monitor changes in microbial biomass within ...subsurface flow wetland mesocosms. The mesocosm hydrolytic activity was referenced to activated sludge concentrations treating a typical domestic wastewater at full scale. Microbial biomass activity levels within four laboratory wetland mesocosms treating a synthetic domestic wastewater were routinely monitored over a 21-week period of plant growth and rhizosphere development. Although above ground plant mass and tracer dispersion numbers suggested progressive root zone development, plant growth did not result in any measurable enhancement in microbial activity when compared to a mesocosm operating without plants. Dispersion numbers also suggested a reduction in the mass transport kinetics in these planted mesocosms. In-situ biomass monitoring enabled the assessment of a characteristic response in terms of the steady-state food to microorganism (F/M) ratio that was observed in mesocosms receiving both low and high organic loading. Wetland treatment performance is sensitive to the degree to which bed volume is exploited in terms of wastewater flow to regions of bioactivity. The in-situ reactive tracer technique for mesocosm biomass monitoring provided an assessment of the collective substratum and rhizosphere microbial biomass in direct contact with wastewater contaminants. Thus, in-situ biomass monitoring has application in further understanding of plant function and strategies for plant implementation in wetland research and development.
PDF
