Carrier surface modification for enhanced attachment and growth of anammox biofilm.

This study investigates and compares the ammonia removal kinetics, attachment, biofilm development and anammox bacteria enrichment on various surface modified carriers throughout the 163 days of start-up of an MBBR system: virgin, dextran-functionalized carriers, silica-functionalized and pre-seeded denitrifying carriers. Silica-functionalized carriers along with pre-seeded denitrifying carriers induced significant higher kinetics, faster biofilm growth and greater anammox bacteria enrichment during the 64 days of operation compared to non-modified virgin and dextran-functionalized carriers. The elevated anammox bacteria counts along with the elevated kinetics of all carriers measured at day 106 indicated that the completed biofilm growth and biofilm maturation are achieved prior to or at day 106 of start-up. The NH4+-N removal rate for virgin, dextran-functionalized, silica-functionalized and pre-seeded denitrifying carriers were achieved 0.684 ± 0.019, 0.608 ± 0.016, 0.634 ± 0.017 and 0.665 ± 0.018 g NH4+-N/m2/d, respectively, at day 106. The results demonstrate that the silica-functionalized and pre-seeded denitrifying carriers offer advantages during the early stage of start-up while the dextran-functionalized carriers did not reduce the start-up period for anammox biofilm.

Anammox attachment and biofilm development on surface-modified carriers with planktonic- and biofilm-based inoculation.

This study investigates the kinetics, attachment, biofilm development and anammox bacteria enrichment of a novel detached anammox biofilm inoculation method on non-modified virgin MBBR carriers and pre-seeded denitrifying carriers. The study compares these results to the more common use of attached anammox carriers for anammox MBBR inoculation. The anammox bacteria specific attachment-growth rates for virgin carriers inoculated with detached anammox biofilm mass were 38.1% greater for the first 25 days, leading to approximately 30% less time required to achieve complete biofilm coverage than those measured in attached biofilm carrier inoculated systems during the attachment and early biofilm growth stages. The biofilm thickness increase rate was also 52.3% higher for virgin carriers with detached biofilm inoculum. Further, inoculation using pre-seeded denitrifying carriers compared to virgin carriers demonstrated a 13.8% preferential increase in anammox bacteria specific attachment-growth rate and a corresponding 47.2% higher NH4+-N removal rate at the time of biofilm maturation.

Consistent production of high quality PHA using activated sludge harvested from full scale municipal wastewater treatment - PHARIO.

Production of polyhydroxyalkanoate (PHA) biopolymers by mixed microbial cultures concurrent to wastewater treatment is a valorization route for residual organic material. This development has been at pilot scale since 2011 using industrial and municipal organic residuals. Previous experience was the basis for a PHA production demonstration project: PHARIO. PHARIO was centred on processing surplus activated sludge biomass from the Bath full-scale municipal wastewater treatment plant in the Netherlands to produce PHA. Full-scale surplus activated sludge was fed to a pilot facility to produce PHA rich biomass using fermented volatile fatty acid (VFA) rich liquors from industry or primary sludge sources. A PHA rich biomass with on average 0.41 gPHA/gVSS was obtained with reproducible thermal properties and high thermal stability. A routine kilogram scale production was established over 10 months and the polymer material properties and market potential were evaluated. Surplus full-scale activated sludge, over four seasons of operations, was a reliable raw material to consistently and predictably produce commercial quality grades of PHA. Polymer type and properties were systematic functions of the mean co-polymer content. The mean co-polymer content was predictably determined by the fermented feedstock composition. PHARIO polymers were estimated to have a significantly lower environmental impact compared to currently available (bio)plastics.

Carbon recovery from wastewater through bioconversion into biodegradable polymers.

Polyhydroxyalkanoates (PHA) are biodegradable polyesters that can be produced in bioprocesses from renewable resources in contrast to fossil-based bio-recalcitrant polymers. Research efforts have been directed towards establishing technical feasibility in the use of mixed microbial cultures (MMC) for PHA production using residuals as feedstock, mainly consisting of industrial process effluent waters and wastewaters. In this context, PHA production can be integrated with waste and wastewater biological treatment, with concurrent benefits of resource recovery and sludge minimization. Over the past 15 years, much of the research on MMC PHA production has been performed at laboratory scale in three process elements as follows: (1) acidogenic fermentation to obtain a volatile fatty acid (VFA)-rich stream, (2) a dedicated biomass production yielding MMCs enriched with PHA-storing potential, and (3) a PHA accumulation step where (1) and (2) outputs are combined in a final biopolymer production bioprocess. This paper reviews the recent developments on MMC PHA production from synthetic and real wastewaters. The goals of the critical review are: a) to highlight the progress of the three-steps in MMC PHA production, and as well to recommend room for improvements, and b) to explore the ideas and developments of integration of PHA production within existing infrastructure of municipal and industrial wastewaters treatment. There has been much technical advancement of ideas and results in the MMC PHA rich biomass production. However, clear demonstration of production and recovery of the polymers within a context of product quality over an extended period of time, within an up-scalable commercially viable context of regional material supply, and with well-defined quality demands for specific intent of material use, is a hill that still needs to be climbed in order to truly spur on innovations for this field of research and development.

A process for polyhydroxyalkanoate (PHA) production from municipal wastewater treatment with biological carbon and nitrogen removal demonstrated at pilot-scale.

A process was developed for biological treatment of municipal wastewater for carbon and nitrogen removal while producing added-value polyhydroxyalkanoates (PHAs). The process comprised steps for pre-denitrification, nitrification and post-denitrification and included integrated fixed-film activated sludge (IFAS) with biofilm carrier media to support nitrification. In a pilot-scale demonstration (500-800L), wastewater treatment performance, in line with European standards, were achieved for total chemical oxygen demand (83% removal) and total nitrogen (80% removal) while producing a biomass that was able to accumulate up to 49% PHA of volatile suspended solids with acetic acid or fermented organic residues as substrates. Robust performance in wastewater treatment and enrichment of PHA-producing biomass was demonstrated under realistic conditions including influent variability during 225days of operation. The IFAS system was found to be advantageous since maintaining nitrification on the biofilm allowed for a relatively low (2days) solids retention time (SRT) for the suspended biomass in the bulk phase. Lower SRT has advantages in higher biomass yield and higher active fraction in the biomass which leads to higher PHA productivity and content. The outcomes show that production of added-value biopolymers may be readily integrated with carbon and nitrogen removal from municipal wastewater.

Polyhydroxyalkanoate (PHA) storage within a mixed-culture biomass with simultaneous growth as a function of accumulation substrate nitrogen and phosphorus levels.

The response of a mixed-microbial-culture (MMC) biomass for PHA accumulation was evaluated over a range of relative nitrogen (N) and phosphorus (P) availabilities with respect to the supply of either complex (fermented whey permeate - FWP) or simpler (acetic acid) organic feedstocks. Fed-batch feed-on-demand PHA accumulation experiments were conducted where the feed N/COD and P/COD ratios were varied ranging from conditions of nutrient starvation to excess. A feast-famine enrichment (activated sludge) biomass, produced in a pilot-scale aerobic sequencing batch reactor on FWP and with a long history of stable PHA accumulation performance, was used for all the experiments as reference material. FWP with N/COD ratios of (2, 5, 15, 70 mg/g all with P/COD = 8 mg/g) as well as simulated FWP with nutrient starvation (N/COD = P/COD = 0) conditions were applied. For the acetic acid accumulations, nutrient starvation as well as N/COD variations (2.5, 5, 50 mg/g all with P/COD = 9 mg/g) and P/COD variations (0.5, 2, 9, 15 mg/g all with N/COD = 10 mg/g) were evaluated. An optimal range of combined N and P limitation with N/COD from 2 to 15 mg/g and P/COD from 0.5 to 3 mg/g was considered to offer consistent improvement of productivity over the case of nutrient starvation. Productivity increased due to active biomass growth of the PHA storing biomass without observed risk for a growth response overtaking PHA storage activity. PHA production with respect to the initial active biomass was significantly higher even in cases of excess nutrient additions when compared to the cases of nutrient starvation. The 24-h PHA productivities were enhanced as much as 4-fold from a base value of 1.35 g-PHA per gram initial active biomass with respect nutrient starvation feedstock. With or without nutrient loading the biomass consistently accumulated similar and significant PHA (nominally 60% g-PHA/g-VSS). Based on results from replicate experiments some variability in the extant biomass maximum PHA content was attributed to interpreted differences in the biomass initial physiological state and not due to changes in feedstock nutrient loading. We found that the accumulation process production rates for mixed cultures can be sustained long after the maximum PHA content of the biomass was reached. Within the specific context of the applied fed-batch feed-on-demand methods, active biomass growth was interpreted to have been largely restricted to the PHA-storing phenotypic fraction of the biomass. This study suggests practical prospects for mixed culture PHA production using a wide range of volatile fatty acid (VFA) rich feedstocks. Such VFA sources derived from residual industrial or municipal organic wastes often naturally contain associated nutrients ranging in levels from limitation to excess.

Impact of physical pre-treatment of source-sorted organic fraction of municipal solid waste on greenhouse-gas emissions and the economy in a Swedish anaerobic digestion system.

Several methods for physical pre-treatments of source sorted organic fraction of municipal solid waste (SSOFMSW) before for anaerobic digestion (AD) are available, with the common feature that they generate a homogeneous slurry for AD and a dry refuse fraction for incineration. The selection of efficient methods relies on improved understanding of how the pre-treatment impacts on the separation and on the slurry's AD. The aim of this study was to evaluate the impact of the performance of physical pre-treatment of SSOFMSW on greenhouse-gas (GHG) emissions and on the economy of an AD system including a biogas plant with supplementary systems for heat and power production in Sweden. Based on the performance of selected Swedish facilities, as well as chemical analyses and BMP tests of slurry and refuse, the computer-based evaluation tool ORWARE was improved as to accurately describe mass flows through the physical pre-treatment and anaerobic degradation. The environmental and economic performance of the evaluated system was influenced by the TS concentration in the slurry, as well as the distribution of incoming solids between slurry and refuse. The focus to improve the efficiency of these systems should primarily be directed towards minimising the water addition in the pre-treatment provided that this slurry can still be efficiently digested. Second, the amount of refuse should be minimised, while keeping a good quality of the slurry. Electricity use/generation has high impact on GHG emissions and the results of the study are sensitive to assumptions of marginal electricity and of electricity use in the pre-treatment.

Sludge minimization in municipal wastewater treatment by polyhydroxyalkanoate (PHA) production.

An innovative approach has been recently proposed in order to link polyhydroxyalkanoates (PHA) production with sludge minimization in municipal wastewater treatment, where (1) a sequencing batch reactor (SBR) is used for the simultaneous municipal wastewater treatment and the selection/enrichment of biomass with storage ability and (2) the acidogenic fermentation of the primary sludge is used to produce a stream rich in volatile fatty acids (VFAs) as the carbon source for the following PHA accumulation stage. The reliability of the proposed process has been evaluated at lab scale by using substrate synthetic mixtures for both stages, simulating a low-strength municipal wastewater and the effluent from primary sludge fermentation, respectively. Six SBR runs were performed under the same operating conditions, each time starting from a new activated sludge inoculum. In every SBR run, despite the low VFA content (10% chemical oxygen demand, COD basis) of the substrate synthetic mixture, a stable feast-famine regime was established, ensuring the necessary selection/enrichment of the sludge and soluble COD removal to 89%. A good process reproducibility was observed, as also confirmed by denaturing gradient gel electrophoresis (DGGE) analysis of the microbial community, which showed that a high similarity after SBR steady-state had been reached. The main variation factors of the storage properties among different runs were uncontrolled changes of settling properties which in turn caused variations of both sludge retention time and specific organic loading rate. In the following accumulation batch tests, the selected/enriched consortium was able to accumulate PHA with good rate (63 mg CODPHA g CODXa(-1) h(-1)) and yield (0.23 CODPHA CODΔS(-1)) in spite that the feeding solution was different from the acclimation one. Even though the PHA production performance still requires optimization, the proposed process has a good potential especially if coupled to minimization of both primary sludge (by its use as the VFA source for the PHA accumulation, via previous fermentation) and excess secondary sludge (by its use as the biomass source for the PHA accumulation).

Methodological issues in life cycle assessment of mixed-culture polyhydroxyalkanoate production utilising waste as feedstock.

Assessing the environmental performance of emerging technologies using life cycle assessment (LCA) can be challenging due to a lack of data in relation to technologies, application areas or other life cycle considerations, or a lack of LCA methodology that address the specific concerns. Nevertheless, LCA can be a valuable tool in the environmental optimisation in the technology development phase. One emerging technology is the mixed-culture production of polyhydroxyalkanoates (PHAs). PHA production by pure microbial cultures has been developed and assessed in several LCAs during the previous decade. Recent developments within mixed-culture PHA production call for environmental assessment to guide in technology development. Mixed-culture PHA production can use the organic content in wastewater as a feedstock; the production may then be integrated with wastewater treatment (WWT) processes. This means that mixed-culture PHA is produced as a by-product from services in the WWT. This article explores different methodological challenges for LCA of mixed-culture PHA production using organic material in wastewater as feedstock. LCAs of both pure- and mixed-culture PHA production were reviewed. Challenges, similarities and differences when assessing PHA production by mixed- or pure-cultures were identified and the resulting implications for methodological choices in LCA were evaluated and illustrated, using a case study with mixed- and pure-culture PHA model production systems, based on literature data. Environmental impacts of processes producing multiple products or services need to be allocated between the different products or services. Such situations occur both in feedstock production and when the studied system is providing multiple functions. The selection of allocation method is shown to determine the LCA results. The type of data used, for electricity in the energy system, is shown to be important for the results, which indicates, a strong regional dependency of results for systems with electricity use as an environmental hot spot. The importance of assessing water use, an environmental impact not assessed by any of the reviewed studies, is highlighted.

Integration of biopolymer production with process water treatment at a sugar factory.

The present investigation has focused on generating a surplus denitrifying biomass with high polyhydroxyalkanoate (PHA) producing potential while maintaining water treatment performance in biological nitrogen removal. The motivation for the study was to examine integration of PHA production into the water treatment and residuals management needs at the Suiker Unie sugar beet factory in Groningen, the Netherlands. At the factory, process waters are treated in nitrifying-denitrifying sequencing batch reactors (SBRs) to remove nitrogen found in condensate. Organic slippage (COD) in waters coming from beet washing is the substrate used for denitrification. The full-scale SBR was mimicked at laboratory scale. In two parallel laboratory scale SBRs, a mixed-culture biomass selection strategy of anoxic-feast and aerobic-famine was investigated using the condensate and wash water from Suiker Unie. One laboratory SBR was operated as conventional activated sludge with long solids retention time similar to the full-scale (SRT >16 days) while the other SBR was a hybrid biofilm-activated sludge (IFAS) process with short SRT (4-6 days) for the suspended solids. Both SBRs were found to produce biomass with augmented PHA production potential while sustaining process water treatment for carbon, nitrogen and phosphorus for the factory process waters. PHA producing potential in excess of 60 percent g-PHA/g-VSS was achieved with the lab scale surplus biomass. Surplus biomass of low (4-6 days) and high (>16 days) solids retention time yielded similar results in PHA accumulation potential. However, nitrification performance was found to be more robust for the IFAS SBR. Assessment of the SBR microbial ecology based on 16sDNA and selected PHA synthase genes at full-scale in comparison to biomass from the laboratory scale SBRs suggested that the full-scale process was enriched with a PHA storing microbial community. However, structure-function relationships based on RNA levels for the selected PHA synthases could not be established and, towards this ambition, it is speculated that a wider representation of PHA synthesases would need to be monitored. Additionally at the factory, beet tail press waters coming from the factory beet residuals management activities are available as a carbon source for PHA accumulation. At pilot scale, beet tail press waters were shown to provide a suitable carbon source for mixed culture PHA production in spite of otherwise being of relatively low organic strength (≤ 10 g-COD/L). A copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV with 15% HV on a molar basis) of high thermal stability and high weight average molecular mass (980 kDa) was produced from the beet tail press water. The mixed culture accumulation process sustained PHA storage with parallel biomass growth of PHA storing bacteria suggesting a strategy to further leverage the utilization of surplus functional biomass from biological treatment systems. Integration of PHA production into the existing factory water management by using surplus biomass from condensate water treatment and press waters from beet residuals processing was found to be a feasible strategy for biopolymer production.

The effects of substrate pre-treatment on anaerobic digestion systems: a review.

Focus is placed on substrate pre-treatment in anaerobic digestion (AD) as a means of increasing biogas yields using today's diversified substrate sources. Current pre-treatment methods to improve AD are being examined with regard to their effects on different substrate types, highlighting approaches and associated challenges in evaluating substrate pre-treatment in AD systems and its influence on the overall system of evaluation. WWTP residues represent the substrate type that is most frequently assessed in pre-treatment studies, followed by energy crops/harvesting residues, organic fraction of municipal solid waste, organic waste from food industry and manure. The pre-treatment effects are complex and generally linked to substrate characteristics and pre-treatment mechanisms. Overall, substrates containing lignin or bacterial cells appear to be the most amendable to pre-treatment for enhancing AD. Approaches used to evaluate AD enhancement in different systems is further reviewed and challenges and opportunities for improved evaluations are identified.

Production of polyhydroxyalkanoates in open, mixed cultures from a waste sludge stream containing high levels of soluble organics, nitrogen and phosphorus.

In this study, the production of polyhydroxyalkanoates (PHAs) from waste activated sludge (WAS) was evaluated. PHAs were produced from fermented WAS pretreated via high-pressure thermal hydrolysis, a stream characterised by high levels of nutrients (approximately 3.5 g N L(-1) and 0.5 g P L(-1)) and soluble organics. PHA-storing organisms were successfully enriched at high organic loading rates (6 g COD(sol) L(-1) d(-1)) under aerobic dynamic feeding in sequencing batch reactors at a sludge retention time of 6 d with a short feast length less than 20% of the cycle, and a maximum substrate concentration during feast of 1 g COD(VFA) L(-1). The biomass enrichment, characterised by a decrease in species evenness based on Lorenz curves, provided a biomass that accumulated 25% PHA on a dry-biomass basis with yields on VFA of 0.4 Cmol Cmol(-1) in batch tests. The PHA consisted of ∼70 mol% 3-hydroxybutyrate and ∼30 mol% 3-hydroxyvalerate, and presented high thermal stability (T(d) = 283-287 °C) and a molecular mass ranging from 0.7 to 1.0 × 10(6) g mol(-1). Overall PHA storage was comparable to that achieved with other complex substrates; however, lower PHA storage rates (0.04-0.05 Cmol PHA(-1) Cmol X(-1) h(-1)) and productivities (3-4 Cmol PHA L(-1) h(-1)) were probably associated with a biomass-growth and high-respiration response induced by high levels of non-VFA organics (40-50% of COD(sol) in feed) and nutrients. PHA production is feasible from pretreated WAS, but the enrichment and accumulation process require further optimisation. A milder WAS pretreatment yielding lower levels of non-VFA organics and readily available nutrients may be more amenable for improved performance.

Substrate-dependent denitrification of abundant probe-defined denitrifying bacteria in activated sludge.

The denitrification capacity of different phylogenetic bacterial groups was investigated on addition of different substrates in activated sludge from two nutrient-removal plants. Nitrate/nitrite consumption rates (CRs) were calculated from nitrate and nitrite biosensor, in situ measurements. The nitrate/nitrite CRs depended on the substrate added, and acetate alone or combined with other substrates yielded the highest rates (3-6 mg N gVSS(-1) h(-1)). The nitrate CRs were similar to the nitrite CRs for most substrates tested. The structure of the active denitrifying population was investigated using heterotrophic CO2 microautoradiography (HetCO2-MAR) and FISH. Probe-defined denitrifiers appeared as specialized substrate utilizers despite acetate being preferentially used by most of them. Azoarcus and Accumulibacter abundance in the two different sludges was related to differences in their substrate-specific nitrate/nitrite CRs. Aquaspirillum-related bacteria were the most abundant potential denitrifiers (c. 20% of biovolume); however, Accumulibacter (3-7%) and Azoarcus (2-13%) may have primarily driven denitrification by utilizing pyruvate, ethanol, and acetate. Activated sludge denitrification was potentially conducted by a diverse, versatile population including not only Betaproteobacteria (Aquaspirillum, Thauera, Accumulibacter, and Azoarcus) but also some Alphaproteobacteria and Gammaproteobacteria, as indicated by the assimilation of 14CO2 by these probe-defined groups with a complex substrate mixture as an electron donor and nitrite as an electron acceptor in HetCO2-MAR-FISH tests.

Characterization of the loosely attached fraction of activated sludge bacteria.

Bacterial biomass was characterised in supernatants from activated sludge from a nutrient removal plant after settling before and after applying gentle shear (G approximately 600 s(-1)). Free-swimming and floc-associated bacteria were quantified by microscopy and their identity was determined by fluorescence in-situ hybridization (FISH). Total cell numbers in the supernatant after settling ranged within 2-9 x 10(7)cells/mL. Most cells (60-70%) were associated with microcolonies or small flocs, which made up 5-10% of the total number of particles. The remaining 30-40% of the cells corresponded to free-swimming, single cells. The small flocs in the supernatants (diameter=2.5-35 microm) accounted only for approximately 1% of the total number of particles; however, they greatly contributed to the total volume of biomass in suspension (57% and 75%). The shear applied (G approximately 600 s(-1)) induced some floc detachment and higher cell numbers in the supernatants (10-70 x 10(7)cells/mL). The identity of bacteria in suspension was as diverse as that in the settled sludge; however, bacteria belonging to Planctomycetes, Firmicutes and Deltaproteobacteria were in higher abundance in the sludge supernatants and were enriched in the supernatants due to gentle shear. Potentially active bacteria were quantified based on the ratio of the number of cells fluorescing with the EUBmix gene probe targeting most bacteria to the total number of cells stained with DAPI. Lower ratios of EUBmix to total cells were measured in the supernatants (50%) than in the settled sludge (80%), suggesting that cells in the dispersed fraction of the sludge were potentially less active than those in the average settleable floc. In conclusion, the attachment properties of bacteria in activated sludge were different among groups, rendering floc fractions more susceptible to detachment and suspension depending on their abundance and activity level.

Production of acylated homoserine lactones by Aeromonas and Pseudomonas strains isolated from municipal activated sludge.

Up to now, the production and role of N-acyl homoserine lactones (AHLs) in activated sludge have been poorly understood. In this study, cross-feeding assays with the reporter strains Agrobacterium tumefaciens NTL4 and Chromobacterium violaceum CV026 were used to investigate AHL signal production by municipal activated sludge samples. AHL signal production was consistently detected from municipal activated sludge when different samples were incubated on nutrient media. From one municipal activated sludge sample, 10 strains producing AHL-like auto inducers were isolated by an overlay technique. 16S rDNA-based phylogenetic analysis showed that eight of the isolates belonged to Aeromonas spp. and two to Pseudomonas spp. Box-PCR indicated that six of these Aeromonas isolates were different strains and the two Pseudomonas strains were identical. The production of AHL or AHL-like compounds by these strains was confirmed by thin layer chromatography and biosensor overlays. The six different Aeromonas strains were found to produce the same set of AHLs, including N-hexanoyl-L-homoserine lactone. These results may indicate the possible presence of AHLs in municipal activated sludge. The potential roles of AHL in this eco system are briefly discussed.

Activated sludge deflocculation under temperature upshifts from 30 to 45 degrees C.

Twelve independent batch experiments (<9h) with fresh municipal activated sludge were conducted to assess the occurrence and the mechanisms of deflocculation under a temperature shift from 30 to 45 degrees C. In each experiment, a transient reactor (2 L) was subjected to the temperature shift and a control reactor was operated at a constant temperature of 30 degrees C. The occurrence of deflocculation was demonstrated by the increase in turbidity and in the concentrations of biopolymers in the sludge supernatant from the transient reactor. The maximum levels of proteins in the supernatants ranged from 53 to 81 mg/L, for DNA from 34 to 36 mg/L, for humic compounds from 20 to 40 mg/L, and for carbohydrates from 21 to 31 mg/L. All the biopolymer concentrations in the control reactor remained below 5-10 mg/L. The release of biopolymers was accompanied by an increase in sludge supernatant conductivity (16-32% increase, up to 1.20 mS/cm), soluble chemical oxygen demand (from 129 to 440 mg/L), total suspended solids (>25 mg/L up to 128 mg/L), and a decrease in the mixed liquor volatile suspended solids (up to 11%). The temperature shift was also found to inhibit microbial metabolism by reducing the sludge biomass substrate removal capacity, as measured by oxygen-uptake rates. The temperature shift had a marginal effect causing sludge lysis (as an increase in beta-galactosidase activity) and had no significant impact on sludge viability (live/dead ratio of bacterial cells). It was concluded that sludge deflocculation under a temperature shift from 30 to 45 degrees C involves the solubilisation of extracellular polymeric substances from the flocs and likely also floc fragmentation. In addition, sludge deflocculation and the inhibition of microbial metabolism explain the poor treatment performance observed in previous continuous reactors under similar temperature shifts.

Effects of temperature transient conditions on aerobic biological treatment of wastewater.

The effects of temperature variations on aerobic biological wastewater treatment were evaluated with respect to treatment efficiency, solids discharges, sludge physicochemical properties and microbiology. The effects of controlled temperature shifts (from 35 degrees to 45 degrees C; from 45 degrees to 35 degrees C) and periodic temperature oscillations (from 31.5 degrees C to 40 degrees C, 6-day period, for 30 days) were assessed in 4 parallel, lab-scale sequencing batch reactors (SBRs) that treated pulp and paper mill effluent. Overall, the temperature shifts caused higher effluent suspended solids (ESS) levels (25-100 mg/L) and a decrease (up to 20%) in the removal efficiencies of soluble chemical oxygen demand (SCOD). Lower ESS levels were triggered by a slow (2 degrees C/day) versus a fast (10 degrees C/12h) temperature shift from 35 degrees to 45 degrees C, but the SCOD removal efficiencies decreased similarly in both cases (from 66+/-3% and 65+/-2% to 49+/-3% and 51+/-3%). Temperature oscillations caused an increased deterioration of the sludge settleability [high sludge volume indices (SVI); low zone settling velocities (ZSV)], high ESS levels and lower SCOD removals. The temperature transients were associated with poor sludge settleability (SVI>100 mL/g MLSS, ZSV<1 cm/min), more negatively charged sludge (up to -0.35+/-0.03 meq/g MLSS), increased filament abundance (approximately 4 to 4.5, subjective scale equivalent to very common), and decreased concentrations of protozoa and metazoa (25,000-50,000 microorganisms/mL sludge). The controlled, periodic temperature oscillations had a slight impact on SCOD removal efficiency (5% decrease), and did not seem to select for robust microorganisms that withstood the temperature shift. Sludge deflocculation and filament proliferation caused by these temperature transients may explain the higher ESS levels.