Conventional and (eco) toxicological assessment of batch partial ozone oxidation and subsequent biological treatment of a tank truck cleaning generated concentrate

This paper compares the treatment efficiencies of direct (pH 7.5) and advanced (pH 11.5) partial ozonation followed by biodegradation for the treatment of tank cleaning wastewater concentrate. Both S_COD and toxicity removal efficiencies are examined and direct ozonation is found to perform better in combined toxicity and S_COD removal. Optimal process performance, i.e. the minimal ozone dosage resulting in a maximal removal of S_COD and toxicity in the final effluent, is reached upon reaction of 500 mg O₃/l for both ozonation processes. This ozone dosage results in 60% S_COD reduction for direct ozonation and 64% S_COD reduction for advanced ozonation. A 79% toxicity reduction was achieved using direct ozonation compared to 53% toxicity reduction for advanced ozonation as measured with the standard Pseudokirchneriella subcapitata algal 72 h growth inhibition test. Short-term methods for biodegradability (respirometry) and toxicity (30 min Vibrio fisheri luminescence inhibition) estimation are evaluated in view of process control. The maximal specific oxygen uptake rate of an activated sludge culture (respirometry) is found to relate to the 5-day biochemical oxygen demand (S_BOD,5) but less to the actual S_COD removal during biodegradation. The 30 min Vibrio fisheri luminescence inhibition test is found to be a good short-term estimator for relative changes in toxicity when compared to the standard P. subcapitata algal 72 h growth inhibition test. The 500 mg O₃/l optimal ozone dosage, as determined from P. subcapitata algal 72 h growth inhibition and S_COD removal, could be retrieved using short-term methods.     

Evaluating the influence of process parameters on soluble microbial products formation using response surface methodology coupled with grey relational analysis

Soluble microbial products (SMPs) present a major part of residual chemical oxygen demand (COD) in the effluents from biological wastewater treatment systems, and the SMP formation is greatly influenced by a variety of process parameters. In this study, response surface methodology (RSM) coupled with grey relational analysis (GRA) method was used to evaluate the effects of substrate concentration, temperature, NH₄⁺-N concentration and aeration rate on the SMP production in batch activated sludge reactors. Carbohydrates were found to be the major component of SMP, and the influential priorities of these factors were: temperature > substrate concentration > aeration rate > NH₄⁺-N concentration. On the basis of the RSM results, the interactive effects of these factors on the SMP formation were evaluated, and the optimal operating conditions for a minimum SMP production in such a batch activated sludge system also were identified. These results provide useful information about how to control the SMP formation of activated sludge and ensure the bioreactor high-quality effluent.     

Aerobic degradation of sulfanilic acid using activated sludge

This paper evaluates the aerobic degradation of sulfanilic acid (SA) by an acclimatized activated sludge. The sludge was enriched for over three months with SA (>500 mg/L) as the sole carbon and energy source and dissolved oxygen (DO, >5 mg/L) as the primary electron acceptor. Effects of aeration rate (0-1.74 L/min), DO concentration (0-7 mg/L) and initial SA concentration (104-1085 mg/L) on SA biodegradation were quantified. A modified Haldane substrate inhibition model was used to obtain kinetic parameters of SA biodegradation and oxygen uptake rate (OUR). Positive linear correlations were obtained between OUR and SA degradation rate (R² ≥ 0.91). Over time, the culture consumed more oxygen per SA degraded, signifying a gradual improvement in SA mineralization (mass ratio of O₂: SA at day 30, 60 and 120 were 0.44, 0.51 and 0.78, respectively). The concomitant release of near stoichiometric quantity of sulphate (3.2 mmol SO₄²⁻ released from 3.3 mmol SA) and the high chemical oxygen demand (COD) removal efficacy (97.1%) indicated that the enriched microbial consortia could drive the overall SA oxidation close to a complete mineralization. In contrast to other pure-culture systems, the ammonium released from the SA oxidation was predominately converted into nitrate, revealing the presence of ammonium-oxidizing bacteria (AOB) in the mixed culture. No apparent inhibitory effect of SA on the nitrification was noted. This work also indicates that aerobic SA biodegradation could be monitored by real-time DO measurement.     

Combined (alkaline + ultrasonic) pretreatment effect on sewage sludge disintegration

The individual effects of alkaline (pH 8-13) and ultrasonic (3750-45,000 kJ/kg TS) pretreatments on the disintegration of sewage sludge were separately tested, and then the effect of combining these two methods at different intensity levels was investigated using response surface methodology (RSM). In the combined pretreatment, ultrasonic treatment was applied to the alkali-pretreated sludge. While the solubilization (SCOD/TCOD) increase was limited to 50% in individual pretreatments, it reached 70% in combined pretreatment, and the results clearly showed that preconditioning of sludge at high pH levels played a crucial role in enhancing the disintegration efficiency of the subsequent ultrasonic pretreatment. By applying regression analysis, the disintegration degree (DD) was fitted based on the actual value to a second order polynomial equation: Y = −172.44 + 29.82X₁ + 5.30 × 10⁻³X₂ − 7.53 × 10⁻⁵X₁X₂ − 1.10X₁² − 1.043 × 10⁻⁷X₂², where X₁, X₂, and Y are pH, specific energy input (kJ/kg TS), and DD, respectively. In a 2D contour plot describing the tendency of DD with respect to pH and specific energy input, it was clear that DD increased as pH increased, but it seemed that DD decreased when the specific energy input exceeded about 20,000 kJ/kg TS. This phenomenon tells us that there exists a certain point where additional energy input is ineffective in achieving further disintegration. A synergetic disintegration effect was also found in the combined pretreatment, with lower specific energy input in ultrasonic pretreatment yielding higher synergetic effect. Finally, in order to see the combined pretreatment effect in continuous operation, the sludge pretreated with low intensity alkaline (pH 9)/ultrasonic (7500 kJ/kg TS) treatment was fed to a 3 L of anaerobic sequencing batch reactor after 70 days of control operation. CH₄ production yield significantly increased from 81.9 ± 4.5 mL CH₄/g COD_added to 127.3 ± 5.0 mL CH₄/g COD_added by pretreatment, and this enhanced performance was closely related to the solubilization increase of the sludge by pretreatment. However, enhanced anaerobic digestion resulted in 20% higher soluble N concentration in the reactor, which would be an additional burden in the subsequent nitrogen removal system.     

Drugs degrading photocatalytically: Kinetics and mechanisms of ofloxacin and atenolol removal on titania suspensions

The conversion of the antibiotic ofloxacin and the β-blocker atenolol by means of TiO₂ photocatalysis was investigated. Irradiation was provided by a UVA lamp at 3.37 × 10⁻⁶ einstein/s photon flux, while emphasis was given on the effect of catalyst type and loading (50-1500 mg/L), initial substrate concentration (5-20 mg/L), initial pH (3-10) and the effect of H₂O₂ (0.07-1.4 mM) as an additional oxidant on substrate conversion and mineralization in various matrices (i.e. pure water, groundwater and treated municipal effluent). Conversion was assessed measuring sample absorbance at 288 and 224 nm for ofloxacin and atenolol, respectively, while mineralization measuring the dissolved organic carbon. Degussa P25 TiO₂ was found to be more active than other TiO₂ samples for either substrate degradation, with ofloxacin being more reactive than atenolol. Conversion generally increased with increasing catalyst loading, decreasing initial substrate concentration and adding H₂O₂, while the effect of solution pH was substrate-specific. Reaction rates, following a Langmuir-Hinshelwood kinetic expression, were maximized at a catalyst to substrate concentration ratio (w/w) of 50 and 15 for ofloxacin and atenolol, respectively, while higher ratios led to reduced efficiency. Likewise, high concentrations of H₂O₂ had an adverse effect on reaction, presumably due to excessive oxidant scavenging radicals and other reactive species. The ecotoxicity of ofloxacin and atenolol to freshwater species Daphnia magna was found to increase with increasing substrate concentration (1-10 mg/L) and exposure time (24-48 h), with atenolol being more toxic than ofloxacin. Photocatalytic treatment eliminated nearly completely toxicity and this was more pronounced for atenolol.     

Analysis of the mechanism of sludge ozonation by a combination of biological and chemical approaches

Using the practical sludge obtained from municipal sewage treatment plants, the mechanism of the sludge ozonation process was systematically investigated by a combination of biological and chemical approaches, including analysis of the changes in biological response by CFU and PCR-DGGE, bio-macromolecular activity and radical scavenging activity. The results indicated that after the sludge was exposed to ozone at less than 0.02 g O₃/g TSS, the DGGE fingerprint remained constant and there was still some enzyme activity, indicating that the sludge solubilization was the main process. At greater than 0.02 g O₃/g TSS, the bacteria began to be broken down and ozone was used to oxidize the bio-macromolecules such as proteins and DNA released from the sludge. Bacteria belonging to ‘G-Bacteria’ were able to conserve their DNA in the presence of less than 0.08 g O₃/g TSS. At levels higher than 0.10 g O₃/g TSS, the disintegration of the sludge matrix became slow and the microbes lost most of their activity, and ozone was used to transform the bio-macromolecules into small molecules. However, at levels higher than 0.14 g O₃/g TSS, the ozone failed to oxidize the sludge efficiently, because several radical scavengers such as lactic acid and SO₄²⁻ were released from the microbial cells in the sludge.     

An assessment of the fate, behaviour and environmental risk associated with sunscreen TiO₂ nanoparticles in UK field scenarios

The fate of Ti was examined in an activated sludge plant serving over 200,000 people. These studies revealed a decrease of 30 to 3.2 μg/L of Ti < 0.45 μm from influent to effluent and a calculated Ti presence of 305 mg/kg DW in wasted sludge. Thus, using sludge as a fertiliser would result in a predicted deposition of up to 250 mg/m² of Ti to soil surfaces using a recommended maximal agricultural application rate. Given the major use of TiO₂ in many industrial and domestic applications where loss to the sewer is possible, this measured Ti was presumed to have been largely TiO₂, a proportion of which will be nanoparticle sized. To assess the behaviour of engineered nanoparticle (ENP) TiO₂ in sewage and toxicology studies, Optisol (Oxonica Materials Ltd) and P25 (Evonik Industries AG), which are representative of forms used in sunscreen and cosmetic products, were used. These revealed a close association of TiO₂ ENPs with activated sludge. Using commercial information on consumption, and removal rates for sewage treatment, predictions were made for river water concentrations for sunscreen TiO₂ ENPs for the Anglian and Thames regions in Southern England. The highest predicted value from these exercises was 8.8 μg/L for the Thames region in which it was assumed that one in four people used the recommended application of sunscreen during a low flow (Q95) period. Ecotoxicological studies using potentially vulnerable species indicated that 1000 μg/L TiO₂ ENP did not affect the viability of a mixed community of river bacteria in the presence of UV light. Direct exposure to TiO₂ ENPs did not impair the immuno-effectiveness of earthworm coelomocyte cells at concentrations greatly above those predicted for sewage sludge.     

Solar treatment of cork boiling and bleaching wastewaters in a pilot plant

This paper reports on cork boiling and bleaching wastewaters treatment by solar photocatalytic processes, TiO₂/UV and Fe²⁺/H₂O₂/UV (TiO₂-only for bleaching wastewater), in a pilot plant with compound parabolic collectors. The photo-Fenton reaction (k = 0.12 L/kJ_UV, r₀ = 59.4 mg/kJ_UV) is much more efficient that TiO₂ photocatalysis and TiO₂ + S₂O₈²⁻ (k = 0.0024 L/kJ_UV, r₀ = 1.36 mg/kJ_UV), leading to 94% mineralization of the bleaching wastewater after 31.5 kJ_UV/L, consuming 77.1 mM of H₂O₂ (3.0 mmol/kJ_UV) and using 20 mg/L of iron. For the cork boiling wastewater, after a slow initial reaction rate, the DOC degradation curve shows a first-order kinetics behaviour (k = 0.015 L/kJ_UV, r₀ = 20.8 mg/kJ_UV) until 173 kJ_UV/L (≈300 mg C/L). According to the average oxidation state (AOS), toxicity profiles, respirometry and kinetic results obtained in two solar CPCs plants, the optimal energy dose estimated for phototreatment to reach a biodegradable effluent is 15 kJ_UV/L and 114 kJ_UV/L, consuming 33 mM and 151 mM of H₂OT:/PGN/ELSEVIER/WR/web/00007490/₂, achieving almost 49% and 48% mineralization of the wastewaters, respectively for the cork bleaching and boiling wastewaters.     

Growth, maintenance and product formation of autotrophs in activated sludge: taking the nitrite-oxidizing bacteria as an example

The autotrophs in activated sludge play an important role in biological wastewater treatment, especially in the nitrification process. Compared with the heterotrophs in activated sludge, information about the growth, maintenance, and product formation of the autotrophs is still sparse. In this work both experimental and modeling approaches are used to investigate the growth, nitrite inhibition, maintenance, and formation of extracellular polymeric substances (EPS) and soluble microbial products (SMP) of the autotrophs, with nitrite-oxidizing bacteria (NOB) in activated sludge as an example. The unified theory for EPS and SMP is integrated into our model to describe the microbial product formation of the NOB. Extensive experiments were carried out using the NOB-enriched in a sequencing batch reactor for the calibration and validation of the developed model. Results show that the NOB spend a considerable amount of energy on maintenance processes. Their apparent growth yield is estimated to be 0.044 mg COD biomass mg⁻¹ N. The model simulations reveal that the concentrations of EPS and SMP in the NOB-enriched culture initially increase, but later decrease gradually, and that the SMP formed in the nitrite oxidation process are biodegradable.     

Degradation models and ecotoxicity in marine waters of two antifouling compounds: Sodium hypochlorite and an alkylamine surfactant

Industrial wastes have a substantial impact on coastal environments. Therefore, to evaluate the impact of cooling water discharges from coastal power plants, we studied the kinetics of the degradative processes and the ecotoxicity of two antifouling products: (1) a classic antifouling product; sodium hypochlorite (NaClO) and (2) an alternative one; aliphatic amines (commercial under the registered trade mark Mexel^®432). To assess the persistence of both compounds the decay of sodium hypochlorite and the primary biodegradation rate of Mexel^®432 were determined in natural seawater at 20 °C. The results indicated a more rapid decay of NaClO than Mexel^®432. The degradation behavior of both chemicals was described following a logistic model, which permitted calculating kinetic parameters such as t₅₀ or t₉₀. The t₅₀ was 1 h and 2 d for NaClO and Mexel^®432, respectively. To evaluate the potential risks of the aforementioned treatments to marine organisms, the acute toxicity of both antifouling products was studied on the microalgae Isochrysis galbana and Dunaliella salina, and on the invertebrate Brachionus plicatilis, using growth inhibition and death tests as toxic response, respectively. For I. galbana, the 96-h EC₅₀ values were 2.91 ± 0.15 mg/L of NaClO and 4.55 ± 0.11 mg/L of Mexel^®432. D. salina showed values of 96-h EC₅₀ of 1.73 ± 0.16 mg/L of NaClO and 7.21 ± 0.1 mg/L of Mexel^®432. Brachionus plicatilis showed a 24-h LC₅₀ of 1.23 ± 0.1 mg/L of NaClO and 3.62 ± 0.37 mg/L of Mexel^®432. Acute toxicity was highly dependent on the chemical and species tested. NaClO presented more toxic effects than Mexel^®432, also B. plicatilis was the most sensitive species in both cases. The lowest NOECs obtained, 0.25 mg/L for NaClO and 2.12 mg/L for Mexel^®432, were similar to the theoretical residual concentrations of these biocides in cooling water discharges. Therefore, these discharges can cause undesirable negative effects upon the aquatic organisms present.     

Biological treatability of dairy wastewaters

Biological treatability of an integrated dairy plant wastewater containing a small fraction of whey-washwaters mixture has been experimentally investigated. Emphasis has been placed on the assessment of the initially inert fraction, S₁ and soluble residual microbial products, S_p. Parallel batch experiments have been conducted to determine the kinetic and stoichiometric coefficients of the degradable COD. The results have shown that the wastewater tested had practically no initially inert fraction, but generated residual microbial products amounting to 6–7% of the initial degradable COD. The results obtained have been fed into a set of equations describing the steady state operation of an activated sludge system with sludge recycle and a relationship indicating the variation of the total effluent COD with the sludge age has been defined for the wastewater tested. It is noted that effluent COD cannot be biologically reduced below 85 mg l⁻¹, regardless of the sludge age, due to generation of residual fractions.     

Characterization of alginate-like exopolysaccharides isolated from aerobic granular sludge in pilot-plant

To understand functional gel-forming exopolysaccharides in aerobic granular sludge, alginate-like exopolysaccharides were specifically extracted from aerobic granular sludge cultivated in a pilot plant treating municipal sewage. The exopolysaccharides were identified by the FAO/WHO alginate identification tests, characterized by biochemical assays, gelation with Ca²⁺, blocks fractionation, spectroscopic analysis as UV-visible, FT-IR and MALDI-TOF MS, and electrophoresis. The yield of extractable alginate-like exopolysaccharides was reached 160 ± 4 mg/g (VSS ratio). They resembled seaweed alginate in UV-visible and MALDI-TOF MS spectra, and distinguished from it in the reactions with acid ferric sulfate, phenol-sulfuric acid and Coomassie brilliant blue G250. Characterized by their high percentage of poly guluronic acid blocks (69.07 ± 8.95%), the isolated exopolysaccharides were capable to form rigid, non-deformable gels in CaCl₂. They were one of the dominant exopolysaccharides in aerobic granular sludge. We suggest that polymers play a significant role in providing aerobic granular sludge a highly hydrophobic, compact, strong and elastic structure.     

Long-term formation of microbial products in a sequencing batch reactor

Activated sludge in a sequencing batch reactor (SBR) is subjected to alternating feast-and-famine conditions, which may result in the enhanced production of microbial products: extracellular polymeric substances (EPS), soluble microbial products (SMP), and internal storage products (X_STO). In this work, the long-term formation of these three microbial products by activated sludge in an SBR is investigated using an expanded unified model with a parallel experimental study. We also use the model to compare the impacts in an SBR to those in a continuous-flow activated sludge system. The model captures all experimental trends for all components with solids retention time (SRT) for global steady state and within a cycle. At an SRT of 20 days, the active microorganisms constitute about 28% of the mixed liquor volatile suspended solids (MLVSS); the remaining biomass is comprised of residual inert biomass (X_I) of 40%, EPS of 31%, and X_STO of ∼1%. The active biomass becomes a smaller fraction with the increasing SRT, while the inert biomass becomes increasingly dominant. For soluble components, effluent chemical oxygen demand (COD) is dominated by SMP, which varies to some degree in a cycle, peaking as external substrate becomes depleted. Within the SBR cycle, external substrate (S) declines strongly in the first part of the cycle, and SMP shows a small peak at the time of S depletion. X_STO is the only biomass component that varies significantly during the cycle. It peaks at the time that the input substrate (S) is depleted. Simulation for a continuous-flow activated sludge system and comparison with an SBR reveals that the constant “famine” conditions of the continuous system lead to lower EPS and X_STO, but higher MLVSS and X_I.     

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD₅/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L⁻¹, 0.48 for BOD₂₁/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS⁻¹ h⁻¹.     

Granulation of activated sludge in a pilot-scale sequencing batch reactor for the treatment of low-strength municipal wastewater

Aerobic granulation of activated sludge was achieved in a pilot-scale sequencing batch reactor (SBR) for the treatment of low-strength municipal wastewater (<200 mg L⁻¹ of COD, chemical oxygen demand). The volume exchange ratio and settling time of an SBR were found to be two key factors in the granulation of activated sludge grown on the low-strength municipal wastewater. After operation of 300 days, the mixed liquor suspended solids (MLSS) concentration in the SBR reached 9.5 g L⁻¹ and consisted of approximate 85% granular sludge. The average total COD removal efficiency kept at 90% and NH₄⁺-N was almost completely depleted (∼95%) after the formation of aerobic granules. The granules (with a diameter over 0.212 mm) had a diameter ranging from 0.2 to 0.8 mm and had good settling ability with a settling velocity of 18-40 m h⁻¹. Three bacterial morphologies of rod, coccus and filament coexisted in the granules. Mathematical modeling was performed to get insight into this pilot-scale granule-based reactor. The modified IWA activated sludge model No 3 (ASM3) was able to adequately describe the pilot-scale SBR dynamics during its cyclic operation.     

Influence of feed concentration on the kinetics of biodegradation of phenol in a continuous stirred reactor

The rate of phenol degradation by activated sludge was studied in a completely mixed continuous-flow reactor with sludge recycle, operated at steady-state conditions at 20°C. Monod kinetics was followed when the influent concentration (C_s°) was kept constant. When using different C_s° levels, the phenol removal rate was found to have an inverse dependence on C_s°. It is suggested that this kinetic anomaly is due to inhibition of the biooxidation by some secondary reaction product(s). A kinetic model based on this concept is able to interpret experimental facts.     

Ammonium adsorption in aerobic granular sludge, activated sludge and anammox granules

The ammonium adsorption properties of aerobic granular sludge, activated sludge and anammox granules have been investigated. During operation of a pilot-scale aerobic granular sludge reactor, a positive relation between the influent ammonium concentration and the ammonium adsorbed was observed. Aerobic granular sludge exhibited much higher adsorption capacity compared to activated sludge and anammox granules. At an equilibrium ammonium concentration of 30 mg N/L, adsorption obtained with activated sludge and anammox granules was around 0.2 mg NH₄-N/g VSS, while aerobic granular sludge from lab- and pilot-scale exhibited an adsorption of 1.7 and 0.9 mg NH₄-N/g VSS, respectively. No difference in the ammonium adsorption was observed in lab-scale reactors operated at different temperatures (20 and 30 °C). In a lab-scale reactor fed with saline wastewater, we observed that the amount of ammonium adsorbed considerably decreased when the salt concentration increased. The results indicate that adsorption or better ion exchange of ammonium should be incorporated into models for nitrification/denitrification, certainly when aerobic granular sludge is used.     

Design parameters for sludge reduction in an aquatic worm reactor

Reduction and compaction of biological waste sludge from waste water treatment plants (WWTPs) can be achieved with the aquatic worm Lumbriculus variegatus. In our reactor concept for a worm reactor, the worms are immobilised in a carrier material. The size of a worm reactor will therefore mainly be determined by the sludge consumption rate per unit of surface area. This design parameter was determined in sequencing batch experiments using sludge from a municipal WWTP. Long-term experiments using carrier materials with 300 and 350 μm mesh sizes showed surface specific consumption rates of 45 and 58 g TSS/(m² d), respectively. Using a 350 μm mesh will therefore result in a 29% smaller reactor compared to using a 300 μm mesh. Large differences in consumption rates were found between different sludge types, although it was not clear what caused these differences. Worm biomass growth and decay rate were determined in sequencing batch experiments. The decay rate of 0.023 d⁻¹ for worms in a carrier material was considerably higher than the decay rate of 0.018 d⁻¹ for free worms. As a result, the net worm biomass growth rate for free worms of 0.026 d⁻¹ was much higher than the 0.009-0.011 d⁻¹ for immobilised worms. Finally, the specific oxygen uptake rate of the worms was determined at 4.9 mg O₂/(g ww d), which needs to be supplied to the worms by aeration of the water compartment in the worm reactor.     

Pathogens in septage in Vietnam

Septage is widely acknowledged as a major source of infectious pathogens while disposal of septage, and the operation and maintenance of septic tanks, is not regulated in many developing countries. Twenty untreated septage and septage sludge samples were taken from Can Tho City, Vietnam to examine their pathogen content, and indicator micro-organisms. Escherichia coli and Enterococcus spp. were detected in all samples, regardless of sludge storage time. Phages were detected in 80% of samples. Salmonella spp. were detected in 70% of the untreated septage and 60% of septage sludge samples. Concentrations of phages and bacteria tested in septage sludge after many years of tank storage were much higher than the expected levels. Helminth ova were present in 95% of untreated septage samples with an average of 450 ova l^− 1, and were detected in all septage sludge samples with an average of 16,000 ova l^− 1. Twelve varieties of helminth ova were identified. More helminth ova varieties in higher concentrations were found in septage than those reported from stool samples. The varieties' frequency ranged from 10% to 50% and Ascaris lumbricoides predominated. Results show that pathogens and indicator micro-organisms, especially helminth ova, accumulate in sludge. Thus helminth ova should be considered when septage sludge is treated and used for agriculture. Proper health protection measures must be applied for people handling septage.     

Biohydrogen production from xylose at extreme thermophilic temperatures (70 °C) by mixed culture fermentation

Biohydrogen production from xylose at extreme thermophilic temperatures (70 °C) was investigated in batch and continuous-mode operation. Biohydrogen was successfully produced from xylose by repeated batch cultivations with mixed culture received from a biohydrogen reactor treating household solid wastes at 70 °C. The highest hydrogen yield of 1.62 ± 0.02 mol-H₂/mol-xylose_consumed was obtained at initial xylose concentration of 0.5 g/L with synthetic medium amended with 1 g/L of yeast extract. Lower hydrogen yield was achieved at initial xylose concentration higher than 2 g/L. Addition of yeast extract in the cultivation medium resulted in significant improvement of hydrogen yield. The main metabolic products during xylose fermentation were acetate, ethanol, and lactate. The specific growth rates were able to fit the experimental points relatively well with Haldane equation assuming substrate inhibition, and the following kinetic parameters were obtained: the maximum specific growth rate (μ_max) was 0.17 h⁻¹, the half-saturation constant (K_s) was 0.75 g/L, and inhibition constant (K_i) was 3.72 g/L of xylose. Intermittent N₂ sparging could enhance hydrogen production when high hydrogen partial pressure (>0.14 atm) was present in the headspace of the batch reactors. Biohydrogen could be successfully produced in continuously stirred reactor (CSTR) operated at 72-h hydraulic retention time (HRT) with 1 g/L of xylose as substrate at 70 °C. The hydrogen production yield achieved in the CSTR was 1.36 ± 0.03 mol-H₂/mol-xylose_sonsumed, and the production rate was 62 ± 2 ml/d·L_reactor. The hydrogen content in the methane-free mixed gas was approximately 31 ± 1%, and the rest was carbon dioxide. The main intermediate by-products from the effluent were acetate, formate, and ethanol at 4.25 ± 0.10, 3.01 ± 0.11, and 2.59 ± 0.16 mM, respectively.