COD and BOD removal from domestic wastewater generated in decentralised sectors

The objective of this work is to study COD and BOD reduction of domestic wastewater using discarded material based mixed adsorbents (mixed adsorbent carbon, MAC and commercial activated carbon, CAC) in batch mode. Under optimum conditions, maximum reduction and maximum COD and BOD reduction achieved using MAC and CAC was 95.87% and 97.45%; and 99.05% and 99.54%, respectively. Results showed that MAC offered potential benefits for COD and BOD removal from wastewater.     

Phosphorus removal characteristics of granular and flocculent sludge in SBR

Aerobic granulation technology has become a novel biotechnology for wastewater treatment. However, the distinct properties and characteristics of phosphorus removal between granules and flocculent sludge are still sparse in enhanced biological phosphorus removal process. Two identical sequencing batch reactors (SBRs) were operated to compare phosphorus removal performance with granular sludge (R1) and flocculate activated sludge (R2). Results indicated that the start-up period was shorter in R2 than R1 for phosphorus removal, which made R2 reach the steady-state condition on day 21, while R1 was on day 25, and R2 released and took up more phosphorus than R1. As a result, the phosphorus removal was around 90% in R2 while 80% in R1 at the steady-state system. The special phosphorus release rate and special phosphorus uptake rate were 8.818 mg P/g volatile suspended solids (VSS)/h and 9.921 mg P/g VSS/h in R2, which were consistently greater than those (0.999 and 3.016 mg P/g VSS/h) in R1. The chemical oxygen demand removal in two reactors was similar. The granular SBR had better solid-separation performance and higher removal efficiency of NH₄⁺–N than flocculent SBR. Denaturing gradient gel electrophoresis of PCR-amplified 16S rDNA fragment analysis revealed that the diversity and the level of phosphorus-accumulating bacteria in flocculent sludge were much more than those in the granular sludge.     

Robustness of sludge enriched with short SBR cycles for biological nutrient removal

In this study, it is proposed that short sequencing batch reactor (SBR) cycles select and maintain a robust and active biomass, able to cope with typical disturbances occurring in wastewater treatment plants. In order to test this hypothesis, an SBR system was subjected to COD, N and P shock loads. It was shown that the sludge enriched in the SBR operated with short cycles was able to rapidly recover from the tested disturbances. COD and N removal recovered within 1–2 days for shock loads of 10 times the standard concentration. The P removal took up to 2–3 sludge ages to fully recover from the COD spike, but the enhanced biological phosphorus removal (EBPR) performance was still able to be totally re-established after each of the tests, even in theoretically adverse conditions for the growth of polyphosphate accumulating organisms.     

Simultaneous COD, nitrogen, and phosphate removal by aerobic granular sludge

Aerobic granular sludge technology offers a possibility to design compact wastewater treatment plants based on simultaneous chemical oxygen demand (COD), nitrogen and phosphate removal in one sequencing batch reactor. In earlier studies, it was shown that aerobic granules, cultivated with an aerobic pulse-feeding pattern, were not stable at low dissolved oxygen concentrations. Selection for slow-growing organisms such as phosphate-accumulating organisms (PAO) was shown to be a measure for improved granule stability, particularly at low oxygen concentrations. Moreover, this allows long feeding periods needed for economically feasible full-scale applications. Simultaneous nutrient removal was possible, because of heterotrophic growth inside the granules (denitrifying PAO). At low oxygen saturation (20%) high removal efficiencies were obtained; 100% COD removal, 94% phosphate (P-) removal and 94% total nitrogen (N-) removal (with 100% ammonium removal). Experimental results strongly suggest that P-removal occurs partly by (biologically induced) precipitation. Monitoring the laboratory scale reactors for a long period showed that N-removal efficiency highly depends on the diameter of the granules.     

The fate of phosphate under anoxic conditions in biological nutrient removal activated sludge systems

The nitrogen removal potential of phosphate accumulating organisms under anoxic conditions has been evaluated using a laboratory scale sequencing batch reactor fed with synthetic wastewater and operated in a sequence of anaerobic, anoxic and aerobic periods. The phosphate uptake rate under anoxic conditions was lower than that under aerobic conditions. However, in the presence of an external substrate such as glucose and acetate, the fate of phosphate was dependent on the substrate type; phosphate release occurred in the presence of nitrate as long as acetate was present and glucose did not cause any phosphate release. The nitrate uptake rate was also much lower with glucose than acetate. The results implied that poly-hydroxyalkanoates could be oxidized by nitrate and phosphate uptake during the anoxic phase should be introduced into process modeling. © Rapid Science Ltd. 1998     

Efficient COD removal and nitrification in an upflow microaerobic sludge blanket reactor for domestic wastewater

The treatment performance of an upflow microaerobic sludge blanket reactor (UMSB) for synthetic domestic wastewater was investigated at two dissolved oxygen (DO) levels, 0.3–0.5 and 0.7–0.9 mg l⁻¹, focusing on nitrification performance. The higher DO level induced complete nitrification of ammonia nitrogen (NH₃–N), achieving chemical oxygen demand and NH₃–N removals of 97 and 92%, respectively. There were consistently significantly higher nitrate nitrogen (NO₃–N) and nitrite nitrogen (NO₂–N) levels in the effluent, with ~66% of newly-produced oxidised nitrogen as NO₂–N. Despite the high nitrification efficiency, only about 23% of the removed NH₃–N amount from the influent was ultimately transformed into oxidised nitrogen due to the simultaneous nitrification-denitrification. Sludge blanket development and granulation occurred simultaneously in the UMSB.     

Long-term population dynamics and in situ physiology in activated sludge systems with enhanced biological phosphorus removal operated with and without nitrogen removal

Quantitative fluorescence in situ hybridization (FISH) and the combination of FISH with microautoradiography (MAR) were used in order to study the long-term population dynamics (2.5 years) and the in situ physiology in two parallel activated sludge pilot systems with enhanced biological phosphorus removal (EBPR). The two systems received the same influent wastewater, but were differently operated (with and without nitrogen removal, respectively). Both systems showed a significant P removal that increased when different substrates (phosphorus (P), acetate and glucose, respectively) were added to the influent wastewater. Rhodocyclus-related bacteria were present in both systems in significant numbers (ranging from 4 to 28%) throughout the whole period. This supports the hypothesis that these bacteria occur in significant numbers in different types of well-operating EBPR activated sludge processes. However, we observed a lower correlation (< 0.5) for the amount of Rhodocyclus-related bacteria to the P content in activated sludge than previous studies (> 0.9). The Actinobacteria were the only additional group of bacteria which showed a similar degree of correlation to the P content in activated sludge as the Rhodocyclus-related bacteria--but only for the system without nitrogen removal. Significant amounts (< or = 12%) of glycogen-accumulating bacteria (GAOs) were detected in the system with nitrogen removal (but not in the other system), but had no, in contrast to previous observations, apparent negative effect on the overall EBPR performance. FISH-MAR indicated that a significant part of the Betaproteobacteria (part of them identified as Rhodocyclus-related bacteria) as well as the Actinobacteria were able to take up 33Pi, [3H]-acetate and [3H]-glucose under anaerobic-aerobic conditions. The contribution of anoxic 33Pi uptake under alternating anaerobic-anoxic conditions was significantly lower. Interestingly, not all Rhodocyclus-related bacteria showed uptake of these three radioactive substrates. This may be due to differences in metabolic state, physiological potential or genotype, not detectable by the present probe set for Rhodocyclus-related bacteria. Comparison of the 33Pi, [3H]-acetate and [3H]-glucose uptake by activated sludge after different fixation and incubation procedures showed that a part of the observed 33Pi uptake may have been caused by a combination of a biological and chemical or biologically induced chemical P adsorption.     

Nitrous oxide production in autotrophic nitrogen removal granular sludge: A modeling study

The sustainability of autotrophic granular system performing partial nitritation and anaerobic ammonium oxidation (anammox) for complete nitrogen removal is impaired by the production of nitrous oxide (N₂O). A systematic analysis of the pathways and affecting parameters is, therefore, required for developing N ₂O mitigation strategies. To this end, a mathematical model capable of describing different N ₂O production pathways was defined in this study by synthesizing relevant mechanisms of ammonium-oxidizing bacteria (AOB), nitrite-oxidizing bacteria, heterotrophic bacteria (HB), and anammox bacteria. With the model validity reliably tested and verified using two independent sets of experimental data from two different autotrophic nitrogen removal biofilm/granular systems, the defined model was applied to reveal the underlying mechanisms of N ₂O production in the granular structure as well as the impacts of operating conditions on N ₂O production. The results show that: (a) in the aerobic zone close to the granule surface where AOB contribute to N ₂O production through both the AOB denitrification pathway and the NH ₂OH pathway, the co-occurring HB consume N ₂O produced by AOB but indirectly enhance the N ₂O production by providing NO from NO ₂ ⁻ reduction for the NH ₂OH pathway, (b) the inner anoxic zone of granules with the dominance of anammox bacteria acts as a sink for NO ₂ ⁻ diffusing from the outer aerobic zone and, therefore, reduces N ₂O production from the AOB denitrification pathway, (c) operating parameters including bulk DO, influent NH ₄ ⁺, and granule size affect the N ₂O production in the granules mainly by regulating the NH ₂OH pathway of AOB, accounting for 34–58% of N ₂O turnover, and (d) the competition between the NH ₂OH pathway and heterotrophic denitrification for nitric oxide leads to the positive role of HB in reducing N ₂O production in the autotrophic nitrogen removal granules, which could be further enhanced in the presence of a proper level of influent organics.     

COD removal from expanded granular sludge bed effluent using a moving bed biofilm reactor and their microbial community analysis

The bioreactor performance of a moving bed biofilm reactor (MBBR) as post-treatment of expanded granular sludge bed (EGSB) effluent was investigated. Moreover, the microbial communities of the two bioreactors during different operation periods were studied. The MBBR was efficient for COD removal with the mean efficiency of 82.4%, and produced an effluent with high and stable quality against shock loading resulting from the low temperature applied to EGSB. The study indicates that the microbial community in the reactors could adapt to perturbations such as influent wastewater characteristics and operation temperature, which is beneficial to maintain efficient and stable COD removal in the combined EGSB-MBBR system. Archaeal 16S rRNA gene sequence analysis indicated the presence of Methanomethylovorans, Methanolinea, Methanoregula boonei, Methanosarcina barkeri, and Methanospirillum hungatei in the EGSB. Bacterial 16S rRNA gene sequence analysis indicated the presence of Runella limosa, Dokdonella, Sphaerotilus, Hydrogenophaga, and Pseudomonas in the MBBR. The EGSB-MBBR system established here could be used as an efficient option for organic matter removal, which holds a great potential in practical applications for nutrients (N and P) removal.     

Formaldehyde removal in the air by six plant systems with or without rhizosphere microorganisms

Abstract

Uptake and in-plant transport of formaldehyde by six plants with or without soil microorganisms were investigated. The capabilities of fresh and boiled leaf extracts to dissipate added formaldehyde were also measured to evaluate formaldehyde metabolism in plant tissues. Results show that when the initial formaldehyde level in air was 0.56?±?0.04?mg·m^?3, the removal rate in the plant-only systems varied from 1.91 to 31.8?μg·h^?1·g^?1 FW (fresh weight). The removal rate of plants in the plant-only systems were ordered as Helianthus annuus Linn > Lycopersicon esculentum Miller > Oryza sativa > Sansevieria trifasciata Prain > Bryophyllum pinnatum > Mesembryanthemum cordifolium L. f. Most reduction of formaldehyde in the air was due to degradation by active components in the plant tissues, of which 4–64% of these were through to be enzymatic reactions. In the microbe-plant systems, formaldehyde removal rates increased by 0.24–9.53 fold compared to the plant-only systems, with approximately 19.6–90.5% of the formaldehyde reduction resulting from microbial degradation. Microorganisms added to the rhizosphere solution enhanced phytoremediation by increasing the downward transport of formaldehyde and its release by roots. Results suggest a new means to screen for efficient plant species that can be used for phytoremediation of indoor air.     

Evaluation of the efficacy of upflow anaerobic sludge blanket reactor in removal of colour and reduction of COD in real textile wastewater

The upflow anaerobic sludge blanket (UASB) reactor was evaluated for its efficacy in decolourization and reduction in chemical oxygen demand (COD) of real textile wastewater (RTW) under different operational conditions. The efficiency of UASB reactor in reducing COD was found to be over 90%. Over 92% of colour removal due to biodegradation was achieved. The activities of the anaerobic granules were not affected during the treatment of textile wastewater. Cocci-shaped bacteria were the dominant group over Methanothrix like bacteria in textile wastewater treatment. Alkalinity, volatile fatty acids (VFA) content and pH in effluents indicated that the anaerobic process was not inhibited by textile wastewater. It is concluded that UASB reactor system can effectively be used in the treatment of textile wastewater for the removal of colour and in the reduction of COD.     

Mixed cultures of Serratia marcescens and Kluyveromyces fragilis for simultaneous protease production and COD removal of whey

AIMS: The aim of this study was to investigate the behaviour of a Serratia marcescens-Kluyveromyces fragilis mixed culture in whey, with the objective of proteases production and organic waste reduction. METHODS AND RESULTS: Discontinuous aerobic fermentations in whey were carried out using individual pure cultures and mixed cultures of S. marcescens and K. fragilis. Cell growth, protease production, lactose and proteins consumption and COD/TOC reduction were monitored. Lactose and protein content of the fermenting medium was almost depleted in the mixed cultures, achieving a reduction in the organic content much higher than in both pure cultures. Interestingly, proteolytic activity in the mixed cultures was similar to that obtained for S. marcescens in pure culture. In addition, protease stability was increased in the mixed cultures. Kinetic models were developed fitting well with the experimental results. CONCLUSIONS: Mixed cultures were found to maintain the achievements of each individual fermentation, yielding a high and stable production of proteases and a significant reduction of COD/TOC. SIGNIFICANCE AND IMPACT OF THE STUDY: Mixed cultures tested in this work have shown a synergistic effect with possible industrial applications. These results lead to a gain in the chain value for enzyme production with an environmentally friendly operation.     

Activated sludge treatment of a xenobiotic with or without a biogenic substrate during start-up and shocks

Lab-scale continuous flow activated sludge systems that were acclimated to 2,4-dichlorphenoxyacetic acid (2,4-D) under sole 2,4-D influent and without sludge wastage, were able to maintain successful 2,4-D treatment when both 2,4-D and a biogenic substrate were fed and the systems operated with finite mean cell residence times (theta(c)). When the systems were fed dual 2,4-D and biogenic substrates and operated with finite theta(c) from the start, treatment of 2,4-D fluctuated noticeably long after acclimation. At the reintroduction of 2,4-D after its absence from the influent for a period of time (2,4-D shock), the systems under both the sole and dual substrate conditions suffered similar treatment losses; the extent of treatment losses was related to the length of 2,4-D absence time. When shocked, systems with sole 2,4-D influent had a slight advantage over dual substrates by showing a faster recovery from shocks with the help of re-acclimation.     

A model for penicillin production with and without temperature shift after the growth phase

Summary A strain of Penicillium chrysogenum producting about 8 g/l of penicillin V, was cultivated in a 10-1 bioreactor. Under carbon (C)-limitation during the production phase a glucose/ammonium sulphate mixture was fed using microprocessor control. When the temperature was shifted from 25° C to 30° C at the end of the active growth phase, the specific penicillin production rate was increased by 30%, while the yield remained constant. Maximal productivity without sporulation was obtained when the net growth rate of the active (respiring and producing) biomass, estimated by measuring the respiration rate under defined conditions, was equal to or higher than 0.004 h^–1. A model was developed for penicillin fermentation during C-limitation possessing the following properties: (1) the model is based on ordinary differential equations; (2) the influence of different nutrients is considered; (3) the model recognizes two cell types (active and inactive); (4) the model describes the influence of a temperature shift at the end of the vigorous growth phase. Offprint requests to: D. Siegmund     

Advanced nitrogen removal without addition of external carbon source in an anaerobic/aerobic/anoxic sequencing batch reactor

Bioprocess and Biosystems Engineering - Advanced nitrogen removal without the addition of external carbon source is challenging in the conventional biological nitrogen removal processes. This study...     

Organics and nitrogen removal and sludge stability in aerobic granular sludge membrane bioreactor

Novel aerobic granular sludge membrane bioreactor (GMBR) was established by combining aerobic granular sludge technology with membrane bioreactor (MBR). GMBR showed good organics removal and simultaneous nitrification and denitrification (SND) performances for synthesized wastewater. When influent total organic carbon (TOC) was 56.8-132.6 mg/L, the TOC removal of GMBR was 84.7-91.9%. When influent ammonia nitrogen was 28.1-38.4 mg/L, the ammonia nitrogen removal was 85.4-99.7%, and the total nitrogen removal was 41.7-78.4%. Moreover, batch experiments of sludge with different particle size demonstrated that: (1) flocculent sludge under aerobic condition almost have no denitrification capacity, (2) SND capacity was caused by the granular sludge, and (3) the denitrification rate and total nitrogen removal efficiency were enhanced with the increased particle size. In addition, study on the sludge morphology stability in GMBR showed that, although some granular sludge larger than 0.9 mm disaggregated at the beginning of operation, the granular sludge was able to maintain the stability of its granular morphology, and at the end of operation, the amount of granular sludge (larger than 0.18 mm) stabilized in GMBR was more than 56-62% of the total sludge concentration. The partial disaggregation of large granules is closely associated with the change of operating mode from sequencing batch reactor (SBR) system to MBR system.     

Simultaneous single-cell protein production and COD removal with characterization of residual protein and intermediate metabolites during whey fermentation by K. marxianus

Cheese whey fermentation with Kluyveromyces marxianus was carried out at 40 °C and pH 3.5 to examine simultaneous single-cell protein production and chemical oxygen demand (COD) removal, determine the fate of soluble whey protein and characterize intermediate metabolites. After 36 h of batch fermentation, the biomass concentration increased from 2.0 to 6.0 g/L with 55 % COD reduction (including protein), whereas soluble whey protein concentration decreased from 5.6 to 4.1 g/L. It was confirmed through electrophoresis (SDS-PAGE) that the fermented whey protein was different from native whey protein. HPLC and GC–MS analysis revealed a change in composition of organic compounds post-fermentation. High inoculum concentration in batch fermentation resulted in an increase in biomass concentration from 10.3 to 15.9 g/L with 80 % COD reduction (including protein) within 36 h with residual protein concentration of 4.5 g/L. In third batch fermentation, the biomass concentration increased from 7.3 to 12.4 g/L with 71 % of COD removal and residual protein concentration of 4.3 g/L after 22 h. After 22 h, the batch process was shifted to a continuous process with cell recycle, and the steady state was achieved after another 60 h with biomass yield of 0.19 g biomass/g lactose and productivity of 0.26 g/L h. COD removal efficiency was 78–79 % with residual protein concentration of 3.8–4.2 g/L. The aerobic continuous fermentation process with cell recycle could be applied to single-cell protein production with substantial COD removal at low pH and high temperature from cheese whey.     

Kinetics of nitrate and sulfate removal using a mixed microbial culture with or without limited-oxygen fed

The biological degradation of nitrate and sulfate was investigated using a mixed microbial culture and lactate as the carbon source, with or without limited-oxygen fed. It was found that sulfate reduction was slightly inhibited by nitrate, since after nitrate depletion the sulfate reduction rate increased from 0.37 mg SO₄ ^2?/mg VSS d to 0.71 mg SO₄ ^2?/mg VSS d, and the maximum rate of sulfate reduction in the presence of nitrate corresponded to 56 % of the non-inhibited sulfate reduction rate determined after nitrate depleted. However, simultaneous but not sequential reduction of both oxy-anions was observed in this study, unlike some literature reports in which sulfate reduction starts only after depletion of nitrate, and this case might be due to the fact that lactate was always kept above the limiting conditions. At limited oxygen, the inhibited effect on sulfate reduction by nitrate was relieved, and the sulfate reduction rate seemed relatively higher than that obtained without limited-oxygen fed, whereas kept almost constant (0.86–0.89 mg SO₄ ^2?/mg VSS d) cross the six R_OS states. In contrast, nitrate reduction rates decreased substantially with the increase in the initial limited-oxygen fed, showing an inhibited effect on nitrate reduction by oxygen. Kinetic parameters determined for the mixed microbial culture showed that the maximum specific sulfate utilization rate obtained (0.098?±?0.022 mg SO₄ ^2?/(mg VSS h)) was similar to the reported typical value (0.1 mg SO₄ ^2?/(mg VSS h)), also indicating a moderate inhibited effect by nitrate.