Sludge Dry Weight Research Articles

Valuable elements in sludge from eight municipal wastewater treatment plants in relation to their recovery potential

BackgroundThe management of sludge from municipal wastewater treatment plants (WWTPs) is a global issue, but also an opportunity for circular reuse. Recent data show that sludge reuse in agriculture has the highest share of all utilization routes in the EU. Council Directive 86/278/EEC on the spreading of sludge in agriculture, adopted more than 35 years ago, is still relevant, notwithstanding the discussion on the need to update it. Extracting critical, strategic, and precious metals and metalloids from sludge is an alternative for sludge reuse, which offers several benefits, such as avoiding the high environmental and health risks associated with using sludge directly in agriculture. Additionally, it allows for the recovery of metals, including those listed as Critical Raw Materials by the European Commission. To implement this alternative, it is necessary to first assess the metal content in the sludge and then develop economically and technically viable technologies. In this study, the content of chemical elements in the sludge of eight full-scale WWTPs in Bulgaria is analysed with focus on: (1) assessing the suitability for agricultural application by evaluating the content of macro- and micronutrients and hazardous metals; (2) assessing the possibility of using the sludge as a source of critical and precious metals.ResultsFor the main nutrients, the following contents as a percentage of the sludge dry weight (DW) were recorded—2.06% to 6% for N, 1.52% to 2.67% for P and 0.47% to 0.81% for K, which are in line with case studies of successful sludge application in agriculture. Only sludge samples from two WWTPs exceeded the permitted limit for hazardous metals and metalloids. On the other hand, of the 21 metal and metalloid constituents listed in the EU Critical and Strategic Material (CRM) list, at least one of the examined samples has a content above 10 mg/kg for 15 elements. The average contents in mg/kgDW of Au (1.1), Al (19,272.9), Mg (6677.6), Ti (1730.9), Ga (20.9) and As (16.6) measured in the investigated WWTPs are among the highest or second highest reported in other countries.ConclusionsThe results of the study show prospects for optimising and improving the reuse of sewage sludge in Bulgaria. Sewage sludge from most WWTPs has potential for agricultural application due to its high nutrient content. Large amounts of accumulated critical and strategic metals, gold and silver are trapped in Bulgarian sewage sludge, indicating that sewage sludge could be considered an alternative source with high potential for these valuable elements.

Powdered activated carbon full-scale addition to the activated sludge reactor of a municipal wastewater treatment plant: Pharmaceutical compounds control and overall impact on the process

Powdered activated carbon (PAC) dosing to a conventional activated sludge (AS) reactor is a low-investment option for controlling pharmaceutical compounds (PhCs) in municipal wastewater treatment, but its advantages and limitations in real operating environments are not fully assessed. A 3-week PAC-AS full-scale test was conducted in an oxidation ditch plant to assess PAC impact on effluent quality (PhCs, dissolved organic carbon (DOC) and other parameters), energy consumption, sludge production and costs. DOC-normalized PAC doses of 0.7–2.6 mgPAC/mgDOC significantly reduced recalcitrant PhC discharge (e.g. by 63–83 % for carbamazepine and 67–69 % for diclofenac), the higher dose yielding a more reliable effluent quality. Effluent quality for total phosphorus, colour, organic matter and transmittance was also enhanced and no interference with nitrification, oxidation-reduction potential or dissolved oxygen in the oxidation ditch was observed, resulting in no energy consumption increase. PAC had no impact on effluent turbidity and mixed liquor suspended solids settleability, showing a positive effect on dewatered sludge dry weight and ultimately a 7–9 % increase on final sludge production. After stopping PAC dosing, PAC remaining in the return sludge presented adsorption capacity for some PhCs until it was completely out of the system. Estimated costs for PAC addition to AS-reactor compare favourably with literature data for PAC and GAC post-treatment and similarly with post-ozonation.

Sludge dewaterability enhancement under low temperature condition with cold-tolerant Bdellovibrio sp. CLL13

The dewatering performance of waste activated sludge (WAS) is generally deteriorated under low temperature due to the increase of viscosity, which would exacerbate the difficulties in sludge treatment and disposal. In this study, the cold-tolerant Bdellovibrio sp. CLL13 was successfully screened for efficient sludge biolysis, and it dramatically improved the sludge dewaterability while no significant biolysis effects were observed for the mesophilic BALO strain at 12 °C. The reduction rates of the sludge capillary suction time (CST), the specific resistance of filtration (SRF), the sludge dry weight, and the fecal coliform bacteria concentration at the optimal reaction time of 14 h were 40.1 ± 0.2%, 69.6 ± 0.7%, 7.7 ± 0.4%, and 78.5 ± 0.4%, respectively, when the mixed liquid suspended solids (MLSS) content was between 10.8 and 29.6 g/L, the input dosage of CLL13 was 8.8 × 106 PFU/mL sludge, and the DO level was 1.2 mg/L. Meanwhile, the viscosity reduction rate, the relative hydrophobicity increasement rate, and the bound water reduction rate were 20.3 ± 1.2%, 6.9 ± 0.7%, and 29.4 ± 1.0%, respectively. The ratios of protein content to polysaccharides content in the extracellular polymeric substances (EPS) decreased significantly. In addition, the degradation of the macromolecular substances in EPS and the increase of the soluble chemical oxygen demand, the total nitrogen, the total phosphorus, and the lactate dehydrogenase levels were observed. Therefore, the cold-tolerant CLL13 induced the sludge biolysis and compromised the negative effects of low temperature on the sludge dewatering performance, which should be beneficial for the efficient WAS biolysis treatment application in the near future under low temperature.

Experimental study on characteristics of consolidation of sludge

Sludge dewatering has become an important issue in the sewage treatment industry. The essence of mechanical dewatering is the consolidation and drainage of sludge. Therefore, it is of great significance to study the consolidation characteristics of sludge to improve the dehydration efficiency. Consolidation tests were carried out on the sludge treated with FeCl3 and Fenton reagent, and the consolidation and permeability characteristics of the treated sludge were studied. The sludge shows ultra-high compressibility. The consolidation coefficient of the untreated sludge is 10−7∼10−6cm2/s. After adding 15% FeCl3 (relative to sludge dry weight), the consolidation coefficient of the sludge increased by 5∼8 times, and reached 10−6∼10−5cm2/s after Fenton reaction treatment. The untreated sludge has obvious time deformation characteristics.

Assessment of extracellular antibiotic resistance genes (eARGs) in typical environmental samples and the transforming ability of eARG

The emergence and spread of antibiotic resistance has pose a huge threat to both human health and environmental ecosystem. However, little is known regarding the pool of ARGs in extracellular DNA (eDNA). In this study ten ARGs (sul1, sul2, tetW, tetX, ermA, ermB, blaTEM, ampC, cat and cmr) and class I integron (intI1) in the sludge from hospital, pharmaceutical industry, wastewater treatment plant (WWTP), and swine manure, and sediment in urban lake in the form of both eDNA and intracellular DNA (iDNA) were evaluated by quantitative polymerase chain reaction (qPCR). The results showed that every gram of sludge dry weight contained from 7.31 × 103 to 1.16 × 1010 copies of extracellular ARGs (eARGs) and from 1.04 × 105 to 2.74 × 1012 copies of intracellular ARGs (iARGs). The sludge from hospital with the highest ratio of eARGs to total ARGs (11.02–89.63%), followed by the sediment from urban lake, implying that most of the ARGs in these regions were contributed by eARGs. The relative abundance of eARGs were higher than iARGs in sludge from WWTP and pharmaceutical industry, moreover, 1/3 and 5/9 detected eARGs were higher than the ARGs in the iDNA extracted from sludge of hospital and sediment from urban lake, respectively. Furthermore, the transforming ability of eARGs suggesting that adsorbed eARG is more preferentially coupled to the competent cells than free eARG. These findings highlight the need to focus attention on the contribution of eARGs to the dissemination of antibiotic resistance into environment, and also future needs in mitigating the spread of eARGs in the environment.

The fate of microplastics in an Italian Wastewater Treatment Plant

The emerged threat of microplastics (MPs) in aquatic ecosystems is posing a new challenges in environmental management, in particular the civil Wastewater Treatment Plants (WWTPs) which can act both as collectors of MPs from anthropic use and as a source to natural environments. In this study, MP fate was investigated in one of the biggest WWTPs of Northern Italy, built at the beginning of the 2000s and which serves a population equivalent of about 1,200,000, by evaluating their presence at the inlet (IN), the removal efficiency after the settler (SET) and at the outlet (OUT), and their transfer to sludge. Samples were collected in three days of a week and plastic debris was characterized in terms of shape, size and polymer composition using the Fourier Transform Infrared Microscope System (μFT-IR). The number of detected MPs was 2.5 ± 0.3 MPs/L in the IN, 0.9 ± 0.3 MPs/L after the SET and 0.4 ± 0.1 MPs/L in the OUT, indicating a total removal efficiency of 84%. However, considering that this WWTP treats about 400,000,000 L wastewaters/day, the potential release of MPs to the receiving aquatic system would be approximately 160,000,000 MPs/day, mainly polyesters (35%) and polyamide (17%). Furthermore, a great amount of MPs removed from wastewater was detected in the recycled activated sludge, with 113 ± 57 MPs/g sludge dry weight, corresponding to about 3,400,000,000 MPs deposited in the 30 tons of sludge daily produced by this WWTP. Given the possible re-use of WWTP sludge in fertilizers for agriculture, our results highlight that WWTPs could represent a potential source of MPs also to agroecosystems.

The Influence of Different Carbon Sources for Polyhydroxyalkanoates Storage

The influence of different carbon sources such as glucose, sodium acetate, sodium propionate and ethanol for polyhydroxyalkanoates (PHA) storage were studied in details. It was shown that both the cell content and composition of PHA synthesized by microorganisms in activated sludge were different when different carbon sources were used. PHB (polyhydroxybutyrate) was the main PHA if sodium acetate was used as carbon source, while PHV (polydroxyvalerate) become the main PHA when sodium propionate was used. Sodium acetate and sodium propionate as carbon source had higher PHA production, which reached to 40.89% and 40.96% sludge dry weight, respectively . When ethanol used as carbon source, PHA content was 25.69% sludge dry weight. The minimal PHA storage was 20.14% sludge dry weight when glucose was used.

Strategy for the biotransformation of fermented palm oil mill effluent into biodegradable polyhydroxyalkanoates by activated sludge

Management of wastewater by resource recovery approach allows the transformation of wastewater into valuable resources. This work examines the biotransformation of fermented palm oil mill effluent (POME) into biodegradable plastics – polyhydroxyalkanoates (PHA) – through cultivation and enrichment of PHA-accumulating organisms in activated sludge and the subsequent production of PHA by the cultivated sludge. Enrichment of PHA-accumulating organisms via aerobic dynamic feeding process was effective and had significantly enhanced the PHA storage capacity of the sludge (wt% PHA per sludge dry weight) from 4wt% (seed sludge) to 40–64wt% (sludge cultivated for 50days and more). The cultivated sludge comprised of 42±12% Betaproteobacteria, 35±7% Alphaproteobacteria, and 13±4% Gammaproteobacteria, as estimated by fluorescent in situ hybridization. The influence of pH (4.5 in the absence of pH control; and pH 7, 8 and 9) on the production of PHA by the cultivated sludge was subsequently investigated. Neutral pH was the most favorable for PHA production, resulting in a PHA content of 64wt% in 8h. The PHA produced was made up of 77mol% 3-hydroxybutyrate and 23mol% 3-hydroxyvalerate. These findings signify that the combination of fermented POME and activated sludge offers an alternative to the palm oil and the plastics industries for a more sustainable POME management and an economical PHA production route.

Influence of temperature on the bioconversion of palm oil mill effluent into volatile fatty acids as precursor to the production of polyhydroxyalkanoates

BACKGROUND The focus of wastewater management has evolved from treatment technology into resource recovery, which enables simultaneous waste minimization and value-added product generation. This study utilized palm oil mill effluent (POME) for volatile fatty acids (VFA) production by acidogenic fermentation at mesophilic (30°C and 40°C) and thermophilic (55°C) temperatures. The viability of using the VFA produced to generate biodegradable plastics polyhydroxyalkanoates (PHA) was also determined. RESULTS The VFA production at mesophilic temperature outperformed thermophilic temperature considerably, with a degree of acidification of 48% at both 30°C and 40°C but only 7% at 55°C. These results were in agreement with the substrate consumption profiles whereby the percentage of substrate consumption at 55°C was six times lower than those at 30°C and 40°C. The VFA produced from POME could be used for PHA production, achieving 17 wt% PHA of sludge dry weight. CONCLUSION Mesophilic acidogenic fermentation of POME is preferable due to its better VFA production. Since palm oil mills are located in tropical countries, the fermentation can be conducted under ambient conditions (25–32°C) and without temperature control. The potential of VFA-rich fermented POME for PHA production is recognized, but optimization of the PHA production conditions is required for higher PHA content. © 2013 Society of Chemical Industry

Sorption of biocides, triazine and phenylurea herbicides, and UV-filters onto secondary sludge

The sludge-water distribution of a total of 41 organic micropollutants (9 phenylurea herbicides, 11 triazines, 16 biocides and 5 UV-filters) was investigated in laboratory batch experiments with fresh secondary sludge taken from a municipal WWTP. Sorption kinetics as well as sorption isotherms were examined by analyzing the compound concentration in the aqueous and solid phase for mass balance control and quality assurance. The sorption kinetic experiments revealed a sorption equilibrium time of <2 h and adverse effects of sodium azide on the sludge-water distribution of several compounds. Sorption isotherms were constructed for 6 different spiking levels spanning 3 orders of magnitude (100 ng L −1–30,000 ng L −1) and were well described by the Freundlich model. For some compounds non-linear sorption with Freundlich exponents n < 1 revealed a decreased sorption affinity to the sludge flocs with increasing aqueous phase concentration. Therefore, sludge-water distribution coefficients ( K d,sec) were calculated from the isotherm data for a constant concentration level of 1 μg L −1. Based on the sludge dry weight (dw), the K d,sec values of phenylurea herbicides ranged from 9 L kg dw sludge −1 (isoproturon) to 320 L kg dw sludge −1 (neburon), those of triazines from 5 L kg dw sludge −1 (atrazine) to 190 L kg dw sludge −1 (terbutryn), those of biocides from 10 L kg dw sludge −1 (N,N-dimethyl-N′-p-tolylsulfamide) to 40,000 L kg dw sludge −1 (triclocarban) and those of UV-filters from 9 L kg dw sludge −1 (phenylbenzimidazole sulfonic acid) to 720 L kg dw sludge −1 (benzophenone-3). For most compounds K d,sec values were below 500 L kg dw sludge −1 and thus removal in WWTPs by the withdrawal of excess sludge is expected to be negligible (<10%) except for the biocides triclocarban (80–95%), triclosan (55–85%), chlorophene (30–60%), imazalil (25–55%) and fenpropimorph (15–40%) as well as the UV-filter benzophenone-3 (5–20%). A simple linear free-energy relationship (LFER) approach using the logarithmized octanol–water partition coefficient log K OW as single descriptor is discussed for a rough classification of nonionic compounds regarding their potential removal in WWTPs by sorption.

Study on poly-hydroxyalkanoate (PHA) production in pilot scale continuous mode wastewater treatment system

Generation of poly-hydroxyalkanoates (PHAs) from milk and ice-cream processing wastewater was studied in a continuous mode reactor system at pilot scale. The integrated system comprised an anaerobic acidogenic reactor (AAR), a conventional activated sludge production reactor (ASPR) and a PHA synthesis reactor (PHAR) to induce PHA accumulation in the biomass which was finally harvested while treating the raw dairy wastewater to meet the disposal limits thereby reducing generation of disposable sludge. The PHA content in the PHA rich biomass was approximately 43% of the sludge dry weight. Kinetics of both ASPR and PHAR were studied. The maximum PHA yield coefficient (Y(sp)(max)) with respect to COD degradation in the PHAR was derived as 0.25 kg PHA/kg of COD degraded. Similarly, the kinetic parameters i.e. K(s), micro(m), Y(obs) and k(d) of the ASPR were 37.16 mg/l COD, 0.97 d(-1), 0.51 mg MLSS/mg COD and 0.049 d(-1), respectively.

Production of polyhydroxyalkanoates by glycogen accumulating organisms treating a paper mill wastewater

A process for production of polyhydroxyalkanoates (PHA) by activated sludge treating a paper mill wastewater was investigated. The applied strategy was to select for glycogen accumulating organisms (GAOs) by alternating anaerobic/aerobic conditions. Acidogenic fermentation was used as pretreatment to convert various organic compounds to volatile fatty acids which are preferable substrates for PHA production. Enrichment resulted in a culture dominated by GAOs related to Defluviicoccus vanus (56%) and Candidatus Competibacter phosphatis (22%). Optimization of PHA accumulation by the enriched GAO culture was performed through batch experiments. Accumulation of PHA under anaerobic conditions was limited by the intracellular glycogen stored. Under aerobic conditions significant glycogen production (to 25% of sludge dry weight) was observed alongside PHA accumulation (to 22% of sludge dry weight). By applying a subsequent anaerobic period after an initial aerobic, the produced glycogen could be utilized for further PHA accumulation and by this strategy PHA content was increased to 42% of sludge dry weight. The PHA yield over the entire process was 0.10 kg per kg of influent COD treated which is similar to what has been achieved with a process applying feast/famine enrichment strategy with the same wastewater.

Production of polyhydroxyalkanoates by activated sludge treating a paper mill wastewater

Production of polyhydroxyalkanoates (PHAs) in activated sludge treating wastewater represents an economical and environmental promising alternative to pure culture fermentations. A process for production of PHA from a paper mill wastewater was examined at laboratory scale. The three stage process examined consisted of acidogenic fermentation to convert wastewater organic matter to volatile fatty acids (VFAs), an activated sludge system operating under feast/famine conditions to enrich for PHA producing organisms and accumulation of PHA in batch experiments. After fermentation of the wastewater, 74% of the soluble COD was present as VFA (acetate, propionate, butyrate and valerate) and the resulting PHA after batch accumulation consisted of 31–47 mol% hydroxybutyrate and 53–69 mol% hydroxyvalerate. The maximum PHA content achieved was 48% of the sludge dry weight and the three stage process exhibited a potential to produce 0.11 kg of PHA per kg of influent COD treated.

Production of polyhydroxyalkanoates (PHA) by activated sludge treating municipal wastewater: effect of pH, sludge retention time (SRT), and acetate concentration in influent

In this paper, the production of biodegradable plastics polyhydroxyalkanoates (PHA) by activated sludge treating municipal wastewater was investigated. The effect of three operational factors, i.e. the acetate concentration in influent, pH, and sludge retention time (SRT) were studied. Sludge acclimatized with municipal wastewater supplemented with acetate could accumulate PHA up to 30% of sludge dry weight, while sludge acclimatized with only municipal wastewater achieved 20% of sludge dry weight. It was found that activated sludge with an SRT of 3 days possessed better PHA production capability than sludge with an SRT of 10 days. Sludge acclimatized under pH 7 and 8 conditions in sequencing batch reactors (SBRs) exhibited similar PHA production capability. However, in PHA production batch experiments, pH value influenced significantly the PHA accumulation behavior of activated sludge. When pH of batch experiments was controlled at 6 or 7, a very low PHA production was observed. The production of PHA was stimulated when pH was kept at 8 or 9.

Characterization of Denitrifying Granular Sludge Treating Soft Groundwater in an Upflow Sludge-Blanket Reactor.

Nitrate removal from soft groundwater using ethanol as a carbon source in an upflow sludge-blanket reactor containing denitrifying granular sludge was investigated. At a hydraulic retention time of 0.83 h, influent nitrate was increased stepwise from 20 to 145 mg N/l (volumetric loading rates (VLRs), 0.60 to 4.2 g N/l/d, respectively) and sludge was periodically wasted to maintain a sludge bed of about 2 3 the liquid volume. Complete nitrate removal was achieved at influent nitrate concentrations up to 75 mg N/l(2.1 g N/l/d). MLSS increased from 20 g/l at a VLR of 0.6 g N/l/d to 51 g/l at a VLR of 1.9 g N/l/d, above which it decreased. VSS increased from 11 g/l to a maximum of 25 g/l at a VLR of 2.1 g N/l/d. Settling velocities showed the same trend with maximum values in a VLR range of 1.5 to 2.1 g N/l/d. However, granule size, calcium and magnesium contents of the granular sludge and protein, carbohydrate and nucleic acid contents of extracellular polymers decreased steadily with an increase in VLR throughout the range of testing. Within the VLR range of 0.6 to 2.1 g N/l/d, corresponding to complete nitrate removal and efficient sludge retention, the granular sludge had a high calcium content of 24 to 22%, magnesium ranged from only 0.7 to 0.1%, proteins from 3.2 to 1.3%, carbohydrates from 4.2 to 1.4%, and nucleic acids from 0.34 to 0.05% of the sludge dry weight. These results suggest an optimum operational VLR in terms of nitrate removal and sludge retention of about 2 g N/l/d.

Characterization of denitrifying granular sludge treating soft groundwater in an upflow sludge-blanket reactor

Nitrate removal from soft groundwater using ethanol as a carbon source in an upflow sludge-blanket reactor containing denitrifying granular sludge was investigated. At a hydraulic retention time of 0.83 h, influent nitrate was increased stepwise from 20 to 145 mg N/ l (volumetric loading rates (VLRs), 0.60 to 4.2 g N/ l/d, respectively) and sludge was periodically wasted to maintain a sludge bed of about 2 3 the liquid volume. Complete nitrate removal was achieved at influent nitrate concentrations up to 75 mg N/ l(2.1 g N/ l/d). MLSS increased from 20 g/ l at a VLR of 0.6 g N/ l/d to 51 g/ l at a VLR of 1.9 g N/ l/d, above which it decreased. VSS increased from 11 g/ l to a maximum of 25 g/ l at a VLR of 2.1 g N/ l/d. Settling velocities showed the same trend with maximum values in a VLR range of 1.5 to 2.1 g N/ l/d. However, granule size, calcium and magnesium contents of the granular sludge and protein, carbohydrate and nucleic acid contents of extracellular polymers decreased steadily with an increase in VLR throughout the range of testing. Within the VLR range of 0.6 to 2.1 g N/ l/d, corresponding to complete nitrate removal and efficient sludge retention, the granular sludge had a high calcium content of 24 to 22%, magnesium ranged from only 0.7 to 0.1%, proteins from 3.2 to 1.3%, carbohydrates from 4.2 to 1.4%, and nucleic acids from 0.34 to 0.05% of the sludge dry weight. These results suggest an optimum operational VLR in terms of nitrate removal and sludge retention of about 2 g N/ l/d.

Microbial community changes in biological phosphate-removal systems on altering sludge phosphorus content.

Biomarkers (respiratory quinones and cellular fatty acids) and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA genes were used to characterize the microbial community structure of lab-scale enhanced biological phosphate-removal (EBPR) systems in response to altering sludge phosphorus (P) content. All the data suggest that the microbial community structures of sludge samples with a P content between 8 and 12.3% (sludge dry weight) (i.e. good EBPR activity) were very similar, but differed from those with 2% P content (i.e. no EBPR activity). For all samples analysed, ubiquinones Q-8 and Q-10, menaquinone MK-8(H4), and fatty acids C16:0, C16:1 omega9c and C18:1, omega11c were the major components. The dominance of Q-8, Q-10 and MK-8(H4) suggested that large numbers of organisms belonging to the beta and alpha subclasses of the Proteobacteria and the Actinobacteria from the high G+C Gram-positive bacteria, respectively, were present. DGGE analysis revealed at least 7-9 predominant DNA bands and numerous other fragments in each sample. Five major DGGE fragments from each of the 2% and 12% P-containing sludge samples, respectively, were successfully isolated and sequenced. Phylogenetic analysis of the sequences indicated that both 2% and 12% P-containing sludge samples shared three common phylotypes that were separately affiliated with a novel bacterial group from the gamma subclass of the Proteobacteria, two MK-8(H4)-containing actinobacteria previously isolated from the 2% P-containing sludge, and a Caulobacter spp. in the alpha subclass of the Proteobacteria. The phylogenetic analysis also revealed phylotypes unique to both sludge samples. Changes in sludge P content therefore had an effect on the composition and abundance of the predominant microbial populations, though specific phylotypes could not be unequivocally associated with EBPR.

Activated sludge as a possible source of biodegradable plastic

Polyhydroxyalkanaote (PHA) is known to be temporarily stored by microorganisms in activated sludge especially in the anaerobic-aerobic processes. When PHA is extracted from activated sludge, it is a thermoplastic with the remarkable characteristics of biodegradability. We investigated the possibility of using activated sludge for the production of PHA, focusing on increasing the PHA content of activated sludge. Activated sludge from laboratory scale anaerobic-aerobic reactors accumulated PHA of around 20% under anaerobic conditions and up to 33% under aerobic conditions. In order to further increase the PHA content of activated sludge, we introduced the “microaerophilic-aerobic” process, where a limited amount of oxygen is supplied into the anaerobic zone of the anaerobic-aerobic process. Activated sludge acclimatized in the microaerophilic-aerobic process accumulated PHA of as much as 62% of sludge dry weight. The “microaerophilic-aerobic” process was demonstrated to be an effective process for the enrichment of PHA-accumulating microorganisms.

Activated sludge as a possible source of biodegradable plastic

Polyhydroxyalkanaote (PHA) is known to be temporarily stored by microorganisms in activated sludge especially in the anaerobic-aerobic processes. When PHA is extracted from activated sludge, it is a thermoplastic with the remarkable characteristics of biodegradability. We investigated the possibility of using activated sludge for the production of PHA, focusing on increasing the PHA content of activated sludge. Activated sludge from laboratory scale anaerobic-aerobic reactors accumulated PHA of around 20% under anaerobic conditions and up to 33% under aerobic conditions. In order to further increase the PHA content of activated sludge, we introduced the “microaerophilic-aerobic” process, where a limited amount of oxygen is supplied into the anaerobic zone of the anaerobic-aerobic process. Activated sludge acclimatized in the microaerophilic-aerobic process accumulated PHA of as much as 62% of sludge dry weight. The “microaerophilic-aerobic” process was demonstrated to be an effective process for the enrichment of PHA-accumulating microorganisms.

Sewage Sludge Components Extractable With Nonaqueous Solvents

AbstractOrganic components in sewage sludges were extracted with nonaqueous solvents (hexane and methanol) and characterized by chromatography, infrared spectroscopy, and mass spectrometry. On the average, nonaqueous solvent soluble compounds represented 10.6% of sludge dry weight (24.8% of ash‐free dry weight) and contained 36% of the total organic C in sludge. Major compounds in nonaqueous solvent extracts included two different waxes, one phenolic fatty acid ester, and a glyceride fatty acid. Significant amounts of dibutyl phthalate, di(2‐ethylhexyl)phthalate, and butyl benzyl phthalate were also present in sludges. The presence of fats, waxes, and oils was expected; however, the presence of phthalate esters in sludges has apparently not been previously reported. The types of phthalate esters in sludge suggest that they are derived from industrial inputs to the municipal sewage treatment system. Polychlorinated biphenyls, polybrominated biphenyls, or chlorinated hydrocarbons were not detected in any of the sludges examined.