ε-Caprolactam-degradation by Alcaligenes faecalis for bioremediation of wastewater of a nylon-6 production plant

Alcaligenes faecalis G utilized 95–97% of 5–15 g -caprolactam l^–1 in 24–48 h over a pH range of 6–8.5 and at 23–40 °C, without complex nutrient requirement. In the absence of KH₂PO₄ and K₂HPO₄/MgSO₄ in the medium, only 7.6% and 0.2% of 10 g caprolactam l^–1 was utilized, respectively. The chemical oxygen demand (COD) of the wastewater of nylon-6 plant was mainly due to its caprolactam content. A. faecalis G decreased the caprolactam content and COD of the wastewater by 80–90% of the original in spite of the wastewater having higher caprolactam content (3600 mg l^–1) and COD (7700 mg l^–1) than those of any of the previous reports.     

Cotton yarn and fabric finishing wastewater treatment in upflow anaerobic filter

Summary Wastewater from cotton yarn and fabric finishing was successfully treated in an upflow anaerobic filter at 35°C up to a COD loading of 1 Kgr COD/m³ · day; the COD removal varied from 50 to 90% and production of biogas was 0,2–0.4 L/g influent COD, having 70–80% CH₄. At higher COD loading biogas production stopped although COD removal remainedca 50%.     

Sequential kinetic parameter estimation of anaerobic fluidized bed bioreactor using an optimization technique

Mathematical model parameters for the methanogenic degradation of propylene glycol were estimated in a sequential manner by means of an optimization technique. Model parameters determined from an initial experimental data set using one bioreactor were then verified with the results from a second bioreactor. The proposed methodology is a useful tool to obtain model parameters for continuous flow reactors with completely mixed regime. Abbrevations: S – substrate concentration (mg COD l^–1); S _in – influent substrate concentration (mg COD l^–1); D _L – dilution rate (day^–1); – stoichiometric coefficients (ND); nx – number of microbial species (ND); X _S – fixed biomass concentration (mg biomass l^–1); X _L – suspended biomass concentration of (mg biomass l^–1); k _d – decay rate of biomass (day^–1); b _S – specific detachment rate of biofilm (day^–1); – specific growth rate of biomass (day^–1); _m – maximum specific growth rate of biomass (day^–1); K _S – half saturation constant (mg COD l^–1); K _I – inhibition constant (mg COD l^–1).     

Influence of bed media characteristics on ammonia and nitrate removal in shallow horizontal subsurface flow constructed wetlands

Two bed media were tested (gravel and Filtralite) in shallow horizontal subsurface flow (HSSF) constructed wetlands in order to evaluate the removal of ammonia and nitrate for different types of wastewater (acetate-based and domestic wastewater) and different COD/N ratios. The use of Filtralite allowed both higher mass removal rates (1.1 g NH₄–N m⁻² d⁻¹ and 3 g NO₃–N m⁻² d⁻¹) and removal efficiencies (>62% for ammonia, 90–100% for nitrate), in less than 2 weeks, when compared to the ones observed with gravel. The COD/N ratio seems to have no significant influence on nitrate removal and the removal of both ammonia and nitrate seems to have involved not only the conventional pathways of nitrification–denitrification. The nitrogen loading rate of both ammonia (0.8–2.4 g NH₄–N m⁻² d⁻¹) and nitrate (0.6–3.2 g NO₃–N m⁻² d⁻¹) seem to have influenced the respective removal rates.     

Nitrification and denitrification in a system of reciprocating jet bioreactor

Concept of separation of stages coupled with novel design of reciprocating jet bioreactor have been incorporated in this research for the development of high efficiency treatment system for contaminated wastewaters.Evaluation of pilot plant data reveals that a three stage reciprocating jet bioreactor system could be effectively employed for nitrification and denitrification of highly polluted wastewater obtained from Berlin wastewater treatment plant. Such a system with COD destruction stage (residence time 1–3 hours) followed by nitrification stage (residence time 3–4.5 hours) and denitrification stage (residence time 0.3 hours) gives COD destruction rate upto 58 kg COD/(m³ day), nitrification rate upto 3.2 NH ₄ ⁺ -N/(m³ day) and denitrification rate upto 28 kg NO ₃ ^– -N/(m³ day) while providing COD, NH ₄ ⁺ -N and NO ₃ ^– -N conversion of more than 90%.Nitrification and denitrification of wastewater at such a short residence time is possible mainly due to the employment of reciprocating jet bioreactor system.Paper presented at the Third Joint Schlesinger Seminar on Transport phenomena and processes in biological systems, Technion — Israel Institute of Technology, Haifa, Israel, May 8–9, 1990     

Biomonitoring of wastewaters in treatment plants using ciliates

The aim of this project has been to study and compare the ciliate populations present in roptating biological reactors treating three different wastewaters. Wastewaters chosen were a maize mill (nejayote), a sugarcane/ethyl alcohol plant (vinasses) and a recycled paper mill (whitewaters). The initial dissolved organic contents, measured as soluble chemical oxygen demand (COD) and biochemical oxygen demand in five days (BOD₅), were 2040±150 mg COD L^–1 and 585±5 mg BOD₅L^–1 for nejayote; 2000±20 mg COD L^–1 and 640±5 mg BOD₅ L^–1 for vinasses and 960±200 mg COD L^–1 and 120±10 mg BOD₅ L^–1 for whitewaters. Results obtained indicate that ciliated protozoa proliferated in the different chambers of each rotating biological reactor (RBR). Saprobity indices, as a quantitative evaluation parameter, indicate that there are no universal species of ciliates associated with specific BOD₅ concentrations. Therefore, the number of species of ciliates present in the effluent indicate qualitatively the efficiency of removal of pollution from the wastewaters during treatment in the rotating biological reactors.     

Continuous cultivation of the yeast Candida utilis at different dilution rates on pineapple cannery effluent

Candida utilis was grown on a pineapple cannery effluent in a chemostat at dilution rates ranging between 0.05 and 0.65 h^–1 to establish optimal conditions for biomass production and chemical oxygen demand (COD) reduction. Sucrose, fructose and glucose were the main sugars in the effluent. Maximum value for cell yield coefficient and productivity were (0.686, g_x/g_s) and (2.96, g_x/l/h) at a dilution rate of 0.425 and 0.475 h^–1, respectively, while maximum COD reduction (98%) was attained at a dilution rate of 0.1 h^–1. The maintenance coefficient attained a value of (0.093, g_s/g_x/h). An increase in dilution rate produced a higher protein content of the biomass.     

Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8-3.1 gCOD/l, 340–850 mgSO₄/l; COD:SO₄ 3.4-5.3) was studied in three laboratory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassays. The reactors were inoculated with non-adapted thermophilic granular sludge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the removed COD was methanised. In the reactors, up to 60–74% COD removal (effluent sulphide stripped) was obtained at loading rates up to 10–30 kgCOD/m³d and hydraulic retention times down to 6 to 2 hours. The effluent total sulphide was up to 150–250 mg/l. Sulphide inhibition could not be confirmed from the reactor performances. The results from bioassays suggested that both the inoculum and sludge from the UASB reactor used acetate mainly for methane production, while sulphide was produced from hydrogen or its precursors.     

Removal of municipal solid waste COD and NH4–N by phyto-reduction: A laboratory–scale comparison of terrestrial and aquatic species at different organic loads

Laboratory scale tests on phytodepuration of raw and pre-treated leachate from municipal sanitary waste were carried out with four vegetable aquatic and terrestrial species at different organic loads. We used the terrestrial species Stenotaphrum secundatum and the free-floating aquatic species Lemna minor, Eichhornia crassipes and Myriophyllum verticellatum to purify leachate from municipal solid waste. The organic load characterized by COD varied from 2–30 g m⁻² day⁻¹. Blanks using tap water served as controls. Duration of the experiments varied from 9–90 days. Maximum concentrations in the experiments were 1600 mg l⁻¹ COD and 300 mg l⁻¹ NH₄–N for S. secundatum. Best results in terms of COD, BOD, and ammonia removal were obtained for raw leachate with COD=2 g m⁻² day⁻¹ in free water surface (FWS) wetlands, and with 2 and 5 g m⁻² day⁻¹ in subsurface flow (SSF) wetlands. Results show that for pretreated leachate (labeled c) low in BOD and NH₄–N, the aquatic species showed low removal and stress even at the lowest load of COD=2 g m⁻² day⁻¹. We cannot say if this is due to the pretreatment itself or the chemical or microbial composition of this leachate. The Stenotaphrum system operated well with this load of leachate c. For untreated leachate (type a and b) the removal and plant growing conditions seemed good at COD=2 g m⁻² day⁻¹. For S. secundatum a load of COD=5 g m⁻² day⁻¹ operated well. All loads above COD=5 g m⁻² day⁻¹ caused low removal and stress, and the green parts of the plants disappeared. Oxygen was, however, consumed throughout the experimental period. For pretreated leachate (type c), the removal of COD were low (−24 to 17%) but good for NH₄–N (52–91%). This leachate also experienced high ammonia removal from the beginning of the experiments, probably due to existing consortia of nitrifying bacteria in it. Statistical analysis shows that the S. secundatum and L. minor systems maintained higher oxygen levels than the M. verticellatum and E. crassipes systems, when operated with tap water. For Lemna minor, this may be due to a better capacity for transporting oxygen into the water. With leachate all S. secundatum systems have higher oxygen levels than the aquatic systems, basically because the water content of the soil has been kept well below saturation. S. secundatum shows a significantly lower removal of COD than did the aquatic systems at a loading of COD=2 g m⁻² day⁻¹ of raw leachate. There is no significant difference between the systems in the removal of NH₄–N at a loading of COD=2 g m⁻² day⁻¹ of both types of leachate. E. crassipes has a lower removal of NH₄–N than M. verticellatum and S. secundatum at a loading of 5 g m⁻² day⁻¹ of COD of both types of leachate. In our experiments, it appears that the amount of free ammonia explains the toxicity of the leachate to the plants. This, however, does not exclude other possible toxic factors.     

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.     

Performance of a hybrid anaerobic reactor,combining a sludge blanket and a filter,treating slaughterhouse wastewater

A column reactor, in which the bottom two-thirds were occupied by a sludge blanket and the upper one-third by submerged clay rings, was evaluated using slaughterhouse wastewater as substrate. The reactor was operated at 35°C at loading rates varying from 5 g to 45 g chemical oxygen demand (COD) 1^–1 × day^–1 at an influent concentration of 2450 mg COD 1^–1. A maximum substrate removal rate of 32 g COD 1^–1 × day^–1, coupled with a methane production rate of 6.91 × 1^–1 × day^–1 (STP), was obtained. This removal rate is significantly higher than those previously reported. The rate of substrate utilization by the biomass was 1.22 g COD (g volatile suspended solids)^–1 day^–1. COD removal was over 96% with loading rates up to 25 g COD 1^–1 × day^–1, at higher loading rates performance decreased rapidly. It was found that the filter element of the reactor was highly efficient in retaining biomass, leading to a biomass accumulation yield coefficient of 0.029 g volatile suspended solids g^–1 COD, higher than reported previously for either upflow anaerobic sludge-blanket reactors or anaerobic filters operating independently.     

Influence of up-flow velocity on the performance of an anaerobic filter under oleic acid overloads

An upflow velocity of 0.21 m h^–1 was optimal to minimize the effect of organic shocks (from 6 to 30 kg COD m^–3 d^–1) when operating an upflow anaerobic filter for the treatment of an oleic acid-based effluent (50% w/v COD). This value represented the transition between a mass transfer controlled regime and a kinetic regime. Under hydraulic shock loads, an increase in upflow velocity from 0.3 to 0.4m h^–1 decreased the removal efficiency from 68 to 51%.     

Methane production from acetamide in an upflow anaerobic sludge-blanket reactor based on a synergistic association between an aerobic rod and methanogens

Acetamide degradation was investigated in a bench-scale upflow anaerobic sludge-blanket (UASB) reactor, successively fed with acetamide, acetate and acetamide, over a period of 343 days, at different hydraulic retention times (t _HR). The reactor was seeded with the sludge previously described [Guyot et al. (1994) Appl Microbiol Biotechnol, 42:452-456], in which methanogenesis from acetamide was performed through a synergistic relationship between an acetamide-degrading, aerobic rod and methanogens. When the reactor was fed acetamide, the chemical oxygen demand (COD) removal efficiency was 86% at volumetric loads less than 1.18 kg COD m^–3 day ^–1. At higher volumetric loads, the efficiency decreased markedly, e.g. 50.9% at a volumetric organic load of 3.39 kg COD m^–3 day^–1 (1 day t _HR) with an accumulation of both acetamide and acetate. The same reactor, when fed with acetate at t _HR 1 day, reached a high COD removal (99%). Evidence of the inhibition of acetate degradation by acetamide is presented. After a long period (135 days) without feeding the reactor with acetamide, the sludge reactor was still capable of degrading acetamide when this substrate was supplied again. It seems that the synergistic degradation of acetamide by aerobes and methanogens present in the UASB reactor sludge is stable over a long period (343 days), in spite of limiting concentrations of dissolved oxygen in the feed.     

The influence of variable organic loading on the start-up of an anaerobic fluidised bed reactor

Summary A stepped-loading start-up regime utilising variable organic influent concentrations in the range 1650–11600 mgCOD1^–1 was applied to an anaerobic fluidised bed bioreactor at 37°C. The reactor was sensitive to variable influent COD concentrations, but the stepped-loading aided rapid recovery from transient organic loading shocks. Variable effluent COD levels were produced but a COD removal efficiency of 76% was obtained at a final HRT of 0.5 d and an organic loading rate of 5.3 kg COD m^–3 d^–1.     

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.     

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).     

Hydrolysis of settleable substrate in domestic sewage

The hydrolysis of settleable substrate in domestic sewage was evaluated using its O₂ utilization rate profile generated in an aerated batch reactor. The hydrolysis rate coefficient was 1.2 d^–1, significantly lower than 3.8 d^–1 and 1.9 d^–1 characterizing soluble and suspended slowly biodegradable fractions. The settled portion of the sewage incorporated an active biomass fraction of 1560 mg COD l^–1 that needed to be accounted for in the hydrolysis kinetics. The texture of the biomass/settled substrate mixture and the gradual hydrolysis of the particulate substrate within the floc structure were examined by microscopic analysis.     

Nitrite reduction by a mixed culture under conditions relevant to shortcut biological nitrogen removal

Dissimilative reduction of nitrite by nitrite-acclimated cellswas investigated in a batch reactor under various environmental conditions that can beencountered in shortcut biological nitrogen removal (SBNR: ammonia to nitrite andnitrite to nitrogen gas). The maximum specific nitrite reduction rate was as much as 4.3 times faster than the rate of nitrate reduction when individually tested, but the reaction was inhibited in the presence of nitrate when the initial nitrate concentration was greater than approximately 25 mg-N/l or the initialNO ₃ ^- N/NO ₂ ^- N ratio was larger than 0.5. Nitrite reduction was also inhibited by nitrite itself when theconcentration was higher than that to which the cells had been acclimated. Therefore, it was desirable to avoid excessively high nitrite and nitrate concentrations in a denitrification reactor. Nitrite reduction, however, was not affected by an alkaline pH (in the range of 7–9) or a high concentration of FA (in the range of 16–39 mg/l), which can be common in SBNR processes. The chemical oxygen demand (COD) requirement for nitrite reduction was approximately 22–38% lower than that for nitrate reduction, demonstrating that the SBNR process can be economical. The specific consumption,measured as the ratio of COD consumed to nitrogen removed, was affected by the availability of COD and the physiological state of the cells. The ratio increased when the cells grew rapidly and were storing carbon and electrons.     

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.     

Removal of organic pollutants and analysis of MLSS–COD removal relationship at different HRTs in a submerged membrane bioreactor

In order to investigate the influence of hydraulic retention time (HRT) on organic pollutant removal in a submerged membrane bioreactor (SMBR), a laboratory-scale experiment was conducted using domestic sewage as influent. The dissolved oxygen (DO) concentration was controlled at 2.0– during the experimental period. The experiments demonstrated that when HRT was 3, 2 and 1 h, the reduction of chemical oxygen demand (COD) was 89.3–97.2, 88.5–97.3 and 80–91.1%, and the effluent COD was 38.9–11.2, 41.6–10.8 and 63.4–, respectively. It is suggested that an HRT of 1 h could meet the normal standard of discharged domestic sewage, and an HRT of 2 h could meet that of water reclamation. In addition, we use mathematical software MATLAB to analyse the relation of mixed liquor suspended solids (MLSS) and COD removal. The results showed that the optimum MLSS concentration should be maintained at around in the SMBR. The results also showed that the COD removal was related to HRT (τ), influent concentration (S₀) and sludge loading rate for COD removal (N_S). Moreover, the high COD removal could be achieved through adjusting τ, S₀ and N_S.