Impact of enzymatic pre-hydrolysis on batch activated sludge systems dealing with oily wastewaters

Dairy wastewater containing different oil and grease contents was treated in batch activated sludge systems with and without (control) an enzymatic pre-hydrolysis stage [with 0.2% (w/v) of fermented babassu cake containing Penicillium restrictum lipases]. When the oil and grease concentration in the control bioreactor was increased (400, 600 and 800 mg l^–1), the COD removal efficiency fell (86%, 75% and 0%). However, in the reactor fed with pre-hydrolysed wastewater, COD removal efficiency was maintained (93%, 92% and 82%). At an oil and grease concentration of 800 mg l^–1, the control bioreactor presented final volatile suspended solids (VSS) values ten times greater (2225 mg l^–1) than those obtained for bioreactor fed with pre-hydrolysed wastewater (200 mg l^–1).     

Enrichment and kinetics of biodegradation of 1-naphthylamine in activated sludge

Sequencing-batch reactors were used to develop an activated sludge enrichment culture capable of degrading 1-naphthylamine (1NA). Approximately 5 months acclimation with salicylic acid (1600 mg l^–1) as the primary source of carbon were required to obtain an enrichment culture able to degrade even small quantities of 1NA. After an additional 4 months acclimation, during which the concentration of salicyclic acid was decreased to 50 mg l^–1, a culture developed that degraded 1NA concentrations as high as 300 mg l^–1. Kinetic determinations showed that 1NA degradation (in the presence of salicylate) followed Michaelis-Menten kinetics with K _m and V _m values of 32.5±2.2 mg l^–1 and 375±18 ng 1NA mg^–1 cells h^–1, respectively. The same enrichement was able to degrade 1NA when present as the sole source of carbon and energy and to convert approximately 87% to CO₂.     

Comparing activated sludge and aerobic granules as microbial inocula for phenol biodegradation

Activated sludge and acetate-fed granules were used as microbial inocula to start up two sequencing batch reactors (R1, R2) for phenol biodegradation. The reactors were operated in 4-h cycles at a phenol loading of 1.8 kg m^–3 day^–1. The biomass in R1 failed to remove phenol and completely washed out after 4 days. R2 experienced initial difficulty in removing phenol, but the biomass acclimated quickly and effluent phenol concentrations declined to 0.3 mg l^–1 from day 3. The acetate-fed granules were covered with bacterial rods, but filamentous bacteria with sheaths, presumably to shield against toxicity, quickly emerged as the dominant morphotype upon phenol exposure. Bacterial adaptation to phenol also took the form of modifications in enzyme activity and increased production of extracellular polymers. 16S rRNA gene fingerprints revealed a slight decrease in bacterial diversity from day 0 to day 3 in R1, prior to process failure. In R2, a clear shift in community structure was observed as the seed evolved into phenol-degrading granules without losing species-richness. The results highlight the effectiveness of granules over activated sludge as seed for reactors treating toxic wastewaters.     

Rapid granulation and sludge retention for tetrachloroethylene removal in an upflow anaerobic sludge blanket reactor

A laboratory scale upflow anaerobic sludge blanket (UASB) reactor was operated at 35 °C for over 200 days to investigate the granulation mechanism during tetrachloroethylene (TCE) biodegradation. Anaerobic, unacclimated sludge and glucose were used as seed and primary substrate, respectively. TCE-degrading granules developed after 1.5 months of start-up. They grew at an accelerated pace for 7 months. The TCE-degrading granules had a maximum diameter of 2.5 mm and specific methanogenic activity of 1.32 g chemical oxygen demand (COD) g^–1 total suspended solid (TSS) day^–1. 94% COD and 90% TCE removal efficiencies were achieved when the reactor was operating at loading rates as high as 160 mg TCE l^–1 day^–1 and 14 g COD l^–1 day^–1, after 230 days of continuous operation.     

Efficiency evaluation of activated sludge treatments of wastewater from fiber board manufacturing

Summary Wastewater from fiber board manufacture consisting in a mixture of Pinus radiata, Eucaliptus globulus and Laureliopsis phillipiana (tepa) (3:1:1) has been studied in laboratory scale activated sludge reactors with organic load rate range of 50–1700 gCOD/m³.d. A stable operation at high organic load rate with hydraulic retention time of one day was achieved. Purification efficiencies up to 90 % of COD removal could be achieved in an activated sludge treatment of fiber board wastewater working with 1 day HRT for wood log cooking wastewater and with 4 days HRT when glueing wastewater is added to the cooking wastewater treatment. Suspended solids, color and phenol concentration were negligible in the efluent of the activated sludge system.     

Isolation and characterization of a phenol-degrading bacterium from an industrial activated sludge

This paper reports the successful isolation and characterization of a new phenol-degrading bacterium, strain EDP3, from activated sludge. Strain EDP3 is a nonmotile, strictly aerobic, Gram-negative, and short-rod or coccobacillary bacterium, which occurs singly, in pairs, or in clusters. 16S rRNA gene sequence analysis revealed that strain EDP3 belonged to the gamma group of Proteobacteria, with a 97.0% identity to 16S rRNA gene sequences of Acinetobacter calcoaceticus. Strain EDP3 could aerobically grow on a number of aromatic compounds, such as phenol, sodium benzoate, p-hydroxybenzoate, phenylacetate, benzene, ethylbenzene, benzylalcohol, and so on. In particular, it could mineralize up to 1,000 mg l⁻¹ phenol at room temperature (25°C). The growth kinetics of strain EDP3 on phenol as a sole carbon and energy source at 25°C can be described using the Haldane equation. It has a maximal specific growth rate (μ_max) of 0.28 h⁻¹, a half-saturation constant (K _S) of 1,167.1 mg l⁻¹, and a substrate inhibition constant (K _i) of 58.5 mg l⁻¹. Values of yield coefficient (Y _X/S) are between 0.4 and 0.6 mg dry cell (mg phenol)⁻¹. Strain EDP3 has high tolerance to the toxicity of phenol (up to 1,000 mg l⁻¹). It therefore could be an excellent candidate for the biotreatment of high-strength phenol-containing industrial wastewaters and for the in situ bioremediation of phenol-contaminated soils.     

Effects of an external magnetic field on the sedimentation of activated sludge

By applying an external magnetic field (800–3000 G, 0.08–0.30 T) using permanent magnets to the aeration vessel of an activated sludge culture, the sedimentation of activated sludge was enhanced and chemical oxygen demand (COD) removal was also improved in an indoor continuous culture system. Adding a small amount of iron(III) chloride (FeCl₃, less than 0.1%, w/v) stimulated these enhancements. The possibility was suggested that the small amount of molecular iron incorporated into the activated sludge stimulated the flocculation and sedimentation by external magnetization.     

Powdered activated carbon added biological treatment of pre-treated landfill leachate in a fed-batch reactor

Biological treatment of landfill leachate usually results in low treatment efficiencies because of high chemical oxygen demand (COD), high ammonium-N content and also presence of toxic compounds such as heavy metals. A landfill leachate with high COD content was pre-treated by coagulation-flocculation followed by air stripping of ammonia at pH = 12. Pre-treated leachate was biologically treated in an aeration tank operated in fed-batch mode with and without addition of powdered activated carbon (PAC). PAC at 2 g l^–1 improved COD and ammonium-N removals resulting in nearly 86% COD and 26% NH₄-N removal.     

Degradation of phenol by a defined mixed culture immobilized by adsorption on activated carbon and sintered glass

Summary A defined mixed culture of the yeast Cryptococcus elinovii H1 and the bacterium Pseudomonas putida P8 was immobilized by adsorption on activated carbon and sintered glass, respectively. Depending on its adsorption capacity for phenol the activated carbon system could completely degrade 17 g/l in batch culture, whereas the sintered glass system was able to degrade phenol up to 4 g/l. During semicontinuous degradation of phenol (1 g/l) both systems reached constant degradation times with the fourth batch that lasted 8 h when using the activated carbon system and 10 h in the sintered glass system. In the course of continuous degradation of phenol the activated carbon system reached a maximum degradation rate of 9.2 g l^–1 day^–1 compared to 6.4 g l^–1 day^–1degraded by the sintered glass system. 2-Hydroxymuconic acid semialdehyde could be identified and quantitatively determined as a metabolite of phenol degradation by P. putida P8. Increased membrane permeability under the influence of phenol was demonstrated by the examination of K⁺ efflux from P. putida P8. Offprint requests to: H.-J. Rehm     

H2 production with anaerobic sludge using activated-carbon supported packed-bed bioreactors

Packed-bed bioreactors containing activated carbon as support carrier were used to produce H₂ anaerobically from a sucrose-limiting medium while acclimated sewage sludge was used as the H₂ producer. The effects of bed porosity (_b) and substrate loading rate on H₂ fermentation were examined using packed beds with _b of 70–90% being operated at hydraulic retention times (HRT) of 0.5–4 h. Higher _b and lower HRT favored H₂ production. With 20 g COD l^–1 of sucrose in the feed, the optimal H₂ production rate (7.4 l h^–1 l^–1) was obtained when the bed with _b=90% was operated at HRT = 0.5 h. Flocculation of cells enhanced the retention of sludge for stable operations of the bioreactor at low HRTs. The gas products resulting from fermentative H₂ production consisted of 30–40% H₂ and 60–70% CO₂. Butyric acid was the primary soluble product, followed by propionic acid and valeric acid.     

Inorganic composition and microbial characteristics of methanogenic granular sludge grown in a thermophilic upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket reactor was operated under thermophilic conditions (55° C) for 160 days by feeding a wastewater containing sucrose as the major carbon source. The reactor exhibited a satisfactory performance due to the formation of well-settling granulated sludge, achieving a total organic carbon (TOC) removal of above 80% at an organic loading rate of 30 kg total organic C m^–3 day^–1. Structural and microbial properties of the methanogenic granular sludge were examined using scanning electron microscope X-ray analyses and serum vial activity tests. All the thermophilic granules developed showed a double-layered structure, comprised of a black core portion and a yellowish exterior portion. The interior cope portion contained abundant crystalline precipitates of calcium carbonate. Calcium-bound phosphorus was also present more prominently in the core portion than in the exterior portion. Methanogenic activities of the thermophilic granules both from acetate and from H₂ increased with increasing vial-test temperature in the range of 55–65° C [from 1.43 to 2.36 kg CH₄ chemical oxygen demand (COD) kg volatile suspended solids (VSS)^–1 day^–1 for acetate and from 0.85 to 1.11 kg CH₄ COD kg VSS^–1 day^–1 for H₂]. On the other hand, propionate-utilizing methanogenic activity was independent of vial-test temperature, and was much lower (0.1–0.12 kg CH₄ COD kg VSS^–1 day^–1) than that from either acetate or H₂. Acetate consumption during vial tests was considerably inhibited by the presence of H₂ in the headspace, indicating that a syntrophic association between acetate oxidizers and H₂-utilizing methane-producing bacteria was responsible for some portion of the overall acetate elimination by the theromophilically grown sludge.     

Tolerance of nitrifying sludge to p-cresol

p-Cresol at 17 mg l^–1 in a nitrifying culture inhibited by 70% nitrate formation whereas at 10 mg l^–1 there was no effect. p-Cresol at 220, 470, and 910 mg l^–1 was converted to intermediates after adaptation times of 8 h, 24 h, and 40 h, respectively. The sludge recovered 44% of its activity after transformation of p-cresol.     

Laboratory-scale evaluation of fluidized bed reactor technology for biotreatment of maleic anhydride process wastewater

Fluidized bed reactor (FBR) technology has emerged in recent years as an attractive approach for the biotreatment of chemical industry wastestreams. A laboratory-scale FBR study was conducted to investigate the feasibility of utilizing FBR technology for the biotreatment of maleic anhydride wastewater generated during manufacturing operations. The maleic anhydride wastestream contains a mixture of maleic acid, fumaric acid, phthalic acid and di-n-butylphthalate (DBP). The FBR removed >98% of chemical oxygen demand (COD) and total organic carbon (TOC) from the wastewater at a chemical loading rate of 4.86 kg of COD m^–3 bed day^–1. Maleic acid, fumaric acid or phthalic acid were not detected in the FBR effluent indicating removal of these diacids. Residues of DBP adsorbed to granular activated carbon (GAC) stabilized at low levels indicating that the >99% removal efficiency for DBP in the FBR resulted from microbial degradation. Solids measurements showed microbial biomass levels on the GAC ranging from 10500 to 32400 mg L^–1 and effluent solids production ranged from 0.027 to 0.041 kg solids kg^–1 COD treated. This laboratory-scale study demonstrated that FBR technology was highly effective for the biotreatment of the maleic anhydride wastestream and may offer several advantages over traditional activated sludge systems.     

Modeling available 2,4-dichlorophenoxyacetic acid in a tissue culture medium containing activated carbon

Clonal propagation of high-value forest trees by somatic embryogenesis can help meet industry needs for uniform and high quality raw materials. Low embryogenic tissue initiation frequencies for loblolly pine (Pinus taeda L.) pose a limitation in work towards commercialization of this technology. At the time our research began most work on somatic embryo culture initiation in loblolly pine reported success in the range of 1–5%. Activated carbon (AC) has been reported to improve many tissue culture systems including embryogenic tissue initiation in Douglas-fir. To improve initiation frequencies in loblolly pine, the development of an AC-containing system was explored. In order to better understand the availability of 2,4-dichlorophenoxyacetic acid (2,4-D) in initiation medium, we tracked media surface concentrations of free or available 2,4-D. Media containing 1/2 modified P6 salts, 1.5% maltose, 2% myo-inositol, case amino acids, glutamine, vitamins, and 0.4% Gelrite were modified to include 0.625 – 2.5 g l^–1 of activated carbon (Sigma C-9157, acid washed) and 110 –440 mg l^–1 2,4-D. Adsorption and availability of 2,4-D in AC-containing medium was tracked by C¹⁴ labeled 2,4-D present in surface moisture absorbed into filter paper. High correlations were found between–available 2,4-D and time when AC and initial 2,4-D concentrations were held constant,–available 2,4-D and AC concentration when initial added 2,4-D and time were held constant, and–available 2,4-D and initial 2,4-D when AC and time were held constant.All of these relationships were exponential, not linear. Multiple regression models inputting initial 2,4-D added to medium in mg l^–1, activated carbon added to medium in %, and time in days, were able to explain 85–88% of the variability in available 2,4-D. These models can be used to achieve target levels of available 2,4-D by adjustment of initial 2,4-D levels or AC content.     

A study on using fireclay as a biomass carrier in an activated sludge system

By adding a biomass carrier to an activated sludge system, the biomass concentration will increase, and subsequently the organic removal efficiency will be enhanced. In this study, the possibility of using excess sludge from ceramic and tile manufacturing plants as a biomass carrier was investigated. The aim of this study was to determine the effect of using fireclay as a biomass carrier on biomass concentration, organic removal and nitrification efficiency in an activated sludge system. Experiments were conducted by using a bench scale activated sludge system operating in batch and continuous modes. Artificial simulated wastewater was made by using recirculated water in a ceramic manufactutring plant. In the continuous mode, hydraulic detention time in the aeration reactor was 8 and 22 h. In the batch mode, aeration time was 8 and 16 h. Fireclay doses were 500, 1,400 and 2,250 mg l⁻¹, and were added to the reactors in each experiment separately. The reactor with added fireclay was called a Hybrid Biological Reactor (HBR). A reactor without added fireclay was used as a control. Efficiency parameters such as COD, MLVSS and nitrate were measured in the control and HBR reactors according to standard methods. The average concentration of biomass in the HBR reactor was greater than in the control reactor. The total biomass concentration in the HBR reactor (2.25 g l⁻¹ fireclay) in the continuous mode was 3,000 mg l⁻¹ and in the batch mode was 2,400 mg l⁻¹. The attached biomass concentration in the HBR reactor (2.25 g l⁻¹ fireclay) in the continuous mode was 1,500 mg l⁻¹ and in the batch mode was 980 mg l⁻¹. Efficiency for COD removal in the HBR and control reactor was 95 and 55%, respectively. In the HBR reactor, nitrification was enhanced, and the concentration of nitrate was increased by 80%. By increasing the fireclay dose, total and attached biomass was increased. By adding fireclay as a biomass carrier, the efficiency of an activated sludge system to treat wastewater from ceramic manufacturing plants was increased.     

Growth inhibition of activated sludge by humus

Humus at 0.5 to 1 mg l–1 inhibited growth of activated sludge by about 55% in batch and long-term repeated batch cultures without decreasing sugar utilization. The growth inhibition was considerable when concentrations of substrates in the medium supplied per unit weight of activated sludge were low.     

Performance of upflow anaerobic sludge blanket (UASB) reactor treating wastewaters containing carbon tetrachloride

The anaerobic biodegradation of carbon tetrachloride (CT) was investigated during the granulation process by reducing the hydraulic retention time, increasing the chemical oxygen demand (COD) and CT loadings in a 2l laboratory-scale upflow anaerobic sludge blanket (UASB) reactor. Anaerobic unacclimated sludge and glucose were used as seed and primary substrate, respectively. Granules were developed 4 weeks after start-up, which grew at an accelerated rate for 8 months, and then became fully grown. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to biomass ratio and specific methanogenic activity (SMA) were also considered during granulation. The granular sludge cultivated had a maximum diameter of 2.1 mm and SMA of 1.6 g COD/g total suspended solid (TSS) day. COD and CT removal efficiencies of 92 and 88% were achieved when the reactor was firstly operating at CT and COD loading rates of 17.5 mg/l day and 12.5 g/l day, respectively. This corresponds to hydraulic retention time of 0.28 day and food to biomass ratio of 0.5 g COD/g TSS day. Kinetic coefficients of maximum specific substrate utilization rate, half velocity coefficient, growth yield coefficient and decay coefficient were determined to be 2.4 × 10^–3 mg CT/TSS day^–1, 1.37 mg CT/l, 0.69 mg TSS/mg CT and 0.046 day^–1, respectively for CT biotransformation during granulation.     

Degrading high-strength phenol using aerobic granular sludge

Aerobic granules were adopted to degrade high-strength phenol wastewater in batch experiments. The acclimated granules effectively degraded phenol at a concentration of up to 5,000 mg l⁻¹ without severe inhibitory effects. The biodegradation of phenol by activated sludge was inhibited at phenol concentrations >3,000 mg l⁻¹. The granules were composed of cells embedded in a compact extracellular matrix. After acid or alkaline pretreatment, the granules continued to degrade phenol at an acceptable rate. The polymerase chain reaction-denaturing gradient gel electrophoresis technique was employed to monitor the microbial communities of the activated sludge and the aerobic granules following their being used to treat high concentrations of phenol in batch tests.     

Substrate consumption and excess sludge reduction of activated sludge in the presence of uncouplers: a modeling approach

A mathematical model with a consideration of energy spilling is developed to describe the activated sludge in the presence of different levels of metabolic uncouplers. The consumption of substrate and oxygen via energy spilling process is modeled with a Monod term, which is dependent on substrate and inhibitor. The sensitivity of the developed model is analyzed. Three parameters, maximum specific growth rate (μ _max), energy spilling coefficient (q _max), and sludge yield coefficient (Y _H) are estimated with experimental data of different studies. The values of μ _max, q _max, and Y _H are found to be 6.72 day^-1, 5.52 day^-1, and 0.60 mg COD mg^-1 COD for 2, 4-dinitrophenol and 7.20 day^-1, 1.58 day^-1, and 0.62 mg COD mg^-1 COD for 2, 4-dichlorophenol. Substrate degradation and sludge yield could be predicted with this model. The activated sludge process in the presence of uncouplers that is described more reasonably by the new model with a consideration of energy spilling. The effects of uncouplers on substrate consumption inhibition and excess sludge reduction in activated sludge are quantified with this model.     

Reducing effect of aerobic selector on the toxicity of synthetic organic compounds in activated sludge process

The effects of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 1,2,4-trichlorobenzene (1,2,4-TCB) on the biodegradation kinetics of the conventional activated sludge system (CASS) and the selector activated sludge system (SASS) were investigated. Experiments were carried out using a respirometric method on unacclimated biomass from two lab-scale systems that were operated with the sludge age of 8 days. Toxicity of the test compounds for both reactors were arranged according to EC₅₀ (effective concentration) values in order as: 1,2,4-TCB > 2,4-DCP > 2-CP > phenol. All selected test compounds induced higher inhibition effect in the CASS. The SASS appeared to reduce inhibition effect in comparison to the CASS, by 21.36%, 66.95%, 64.37% and 33.33% for phenol, 2-CP, 2,4-DCP and 1,2,4-TCB, respectively. Consequently, the SASS may be recommended as a promising configuration alternative for the waste streams containing toxic compounds.