An integrated model of substrate clogging in vertical flow constructed wetlands

This paper presents an integrated model of substrate clogging in a vertical flow constructed wetland (VFCW). The model simulates the reduction of pore space in the wetland substrate due to combined influences of various physical, biogeochemical and plant-related processes. A series of experiments based on laboratory-scale VFCWs were conducted to examine and measure key parameters related to clogging of the wetland substrate during operation under different conditions. The model was then validated using data collected from the experiments. The results showed that the model was able to replicate the clogging phenomenon as observed in the experiments, in particular, the characteristic clogging time. The model also predicted well individual contributions to clogging by accumulated inert suspended solids, microbial biomass and plant root materials during the wetland operation. Although the validation was based on the laboratory data, the results indicated that the model describes well the processes underlying the clogging and has the potential to become a tool for assessing the performance of prototype CWs in relation to clogging at both the design and operation stages.

First Report of Seedling Blight of Watermelon Caused by Acidovorax citrulli Transmitted from Rootstock of Pumpkin in China

Bacterial fruit blotch (BFB) is a devastating disease caused by Acidovorax citrulli, which was first observed in the United States in 1988 (3). A. citrulli can cause severe infection on a wide range of cucurbits, including watermelon, cantaloupe, and pumpkin. Cotyledon symptoms are brown, angular, necrotic spots or large necrotic lesions. The disease is seedborne, so seeds usually serve as the primary inoculum source for BFB outbreaks (2). In July 2012, seedling blight was observed by local farmers from Anhui province in China on watermelon seedlings grafted to pumpkin rootstocks; lesions were morphologically similar to those caused by A. citrulli. Presence of A. citrulli was detected in symptomatic samples by using species-specific primers BX-L1/BX-S-R2 (1). The seed company claimed seeds of watermelon (cv. Changfeng) were certified free of bacterial fruit blotch, but pumpkin seeds (cv. Kangkuxianfeng-1) had not been tested for A. citrulli. For investigating the inoculum source, the remaining seeds of watermelon (cv. Changfeng) and pumpkin (cv. Kangkuxianfeng-1) for seedling production were collected from the farmer and processed for pathogen extraction as described by Walcott and Gitaitis (2). Two microliters of seed wash was used as template for PCR using primers BX-L1/BX-S-R2 (1). The experiment was conducted three times. A 279-bp DNA fragment was consistently amplified by PCR from seed wash of pumpkin seeds, but not from the seed wash of watermelon seeds. Three Acidovorax-like strains (A1, A2, and A3) were isolated from pumpkin seed wash using TWZ semi-selective medium (0.5% peptone, 0.025% CaCl₂, 1% Tween-80, 50 mg/liter berberine, 50 mg/liter cycloheximide, 50 mg/liter 2,3,5-triphenyltetrazolium chloride). PCR was performed on the 16S rDNA gene from isolate strain A1, A2, and A3 (1,492 bp; GenBank Accession Nos. JX875533, JX875534, and JX875535) with primers rp1/fd2 (4), and PCR products were sequenced. Results of sequence analysis showed the sequences of strains A1, A2, and A3 were 99% identical to that of the type strain of A. citrulli AAC00-1 (NC_008752). Pathogencity was confirmed by injection of pumpkin cotyledons with bacterial suspensions of each isolate. Collected pumpkin seeds (n = 100 seeds) and watermelon seeds (n = 100 seeds) were planted in plastic pots containing sterilized field soil at room temperature to detect A. citrulli by a wet chamber growing out test. Eight days later, brown, angular, necrotic spots or wilt developed in pumpkin seedlings, but no symptoms were noted on the watermelon seedlings. To our knowledge, this is the first report of A. citrulli causing watermelon seedling blight transmitted from pumpkin seeds by grafting in China. References: (1) O. Bahar et al. Plant Pathol. 57:754, 2008. (2) R. R. Walcott and R. D. Gitaitis. Plant Dis. 84:470, 2000. (3) G. C. Wall et al. Phytopathology 78:1605, 1988. (4) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991.

Phosphorus recovery as AlPO4 from beneficially reused aluminium sludge arising from water treatment

The purpose of this study was to develop an efficient and, possibly, a practically operated methodology to recover phosphorus (P) from P-saturated dewatered aluminium sludge cakes (DASC) after the DASC have been beneficially reused as constructed wetlands substrate for P-rich wastewater treatment. A three-step procedure of 1) P extraction by H2SO4, 2) decolorization of extraction leachate via H2O2 oxidation, and 3) AlPO4 precipitation by pH adjustment, has been explored. The optimal conditions to form the precipitates of AlPO4 were determined, with 97% of P and 99% of Al being recovered. The obtained compounds were identified by XRD, FTIR and SEM analyses. Although the purity, structure, characteristics and production control of the compounds are worthy of further investigation, this study provides a showcase of a 'closed loop' regarding the beneficial reuse of a 'waste' and the recovery of useful elements after the reuse.

Comprehensive analysis of step-feeding strategy to enhance biological nitrogen removal in alum sludge-based tidal flow constructed wetlands

Step-feeding strategies have been extensively studied and comprehensively analyzed in this study for a four-stage alum sludge-based tidal flow constructed wetlands (AlS-TFCWs) system. Enhanced total nitrogen removal of 83% is achieved under high nitrogen loading rate of 19.1 g N/m(2)d. The key issues towards the success of a significant nitrogen removal in step-feeding TFCWs are the bed resting time (which provides better aeration for nitrification) and up flow stage/delayed input of side stream(s) (which ensure favorable environment for better denitrification). Simultaneous nitrification and denitrification (SND) was found effective in the 1st stage of the system and SND via nitrite is the main nitrogen conversion mechanism. The optimal influent distribution fraction for step-feeding purpose can be estimated from a theoretical basis, which is a function of the influent BCOD/TKN ratio. Therefore the influent distribution fraction should be adjusted according to the variety of influent characteristics, rather than a fixed value.

Effects of livestock wastewater variety and disinfectants on the performance of constructed wetlands in organic matters and nitrogen removal

BACKGROUND, AIM AND SCOPE

Treatment performance of constructed wetlands (CWs) is largely dependent on the characteristics of the wastewater. Although livestock wastewater is readily biodegradable in general, its variety in biodegradability can still be significant in practice. In addition, it is a common practice to periodically use disinfectants in livestock activities for health concerns. Obviously, the residual of the disinfectants in livestock wastewater may have serious inhibitory effect on the microbial activities during wastewater treatment. Thus, the main objective of this study was to examine the variety of livestock wastewater in biodegradability and its effect on the performance of a pilot scale tidal flow CWs (TFCWs) in organic matter and nitrogen removal. Furthermore, investigation of the potential inhibition of the chosen disinfectants on organic matter biodegradation and nitrification was another aim of this study.

MATERIALS AND METHODS

The TFCWs system consisted of four-stage downflow reed beds with a hydraulic loading rate of 0.29 m(3)/m(2)·per day. Long-term stored livestock wastewater and fresh livestock wastewater were used, respectively, as feed to the system in different periods. Meanwhile, batch aeration tests were carried out to investigate the difference in biodegradation of the two types of wastewaters. Inhibitions of two types of disinfectants, namely UNIPRED and HYPROCLOR ED, on microbial activities were investigated in laboratory batch tests, with dosage of from 0.05% to 0.5%.

RESULTS

With fresh livestock wastewater, removal efficiencies of up to 93% and 94% could be achieved with average of 73% and 64% for chemical oxygen demand (COD) and TN, respectively. The performance deteriorated when the system was fed with long-term stored wastewater. In the batch tests, the long-time stored wastewater was characterized as non-biodegradable or at least very slowly biodegradable, while the fresh wastewater was readily biodegradable. UNIPRED showed very strong inhibition on both heterotrophic organisms and nitrifiers. Tested inhibition started from content of 0.05%, which is 1/10 of the recommended usage rate. Inhibitory effect of HYPROCLOR ED on COD degradation started from 0.1% and complete inhibition occurred from content of 0.3%, while significant inhibition on nitrification started from 0.1%.

CONCLUSIONS

Livestock wastewater could vary significantly in biodegradability and it may turn to be non-biodegradable after a long-term storage. The variety of the livestock wastewater has a decisive influence on the performance of the CWs system, especially in TN elimination. In addition, the application of disinfectants UNIPRED and HYPROCLOR ED may cause serious inhibition on microbial activities and subsequent system failure.

Performance evaluation and prediction for a pilot two-stage on-site constructed wetland system employing dewatered alum sludge as main substrate

Dewatered alum sludge, a widely generated by-product of drinking water treatment plants using aluminium salts as coagulants was used as main substrate in a pilot on-site constructed wetland system treating agricultural wastewater for 11 months. Treatment performance was evaluated and spreadsheet analysis was used to establish correlations between water quality variables. Results showed that removal rates (in g/m(2)d) of 4.6-249.2 for 5 day biochemical oxygen demand (BOD(5)), 35.6-502.0 for chemical oxygen demand (COD), 2.5-14.3 for total phosphorus (TP) and 2.7-14.6 for phosphate (PO(4)P) were achieved. Multiple regression analysis showed that effluent BOD(5) and COD can be predicted to a reasonable accuracy (R(2)=0.665 and 0.588, respectively) by using input variables which can be easily monitored in real time as sole predictor variables. This could provide a rapid and cheap alternative to such laborious and time consuming analyses and also serve as management tools for day-to-day process control.

A review on numerous modeling approaches for effective, economical and ecological treatment wetlands

Constructed wetlands (CWs) for wastewater treatment have evolved substantially over the last decades and have been recognized as an effective means of "green technology" for wastewater treatment. This paper reviews the numerous modeling approaches ranging from simple first-order models to more complex dynamic models of treatment behaviour in CWs. The main objective of the modeling work is to better understand the process in CWs and optimize design criteria. A brief study in this review discusses the efforts taken to describe the process-based model for the efficient removal of pollutants in CWs. Obtaining better insights is essential to understand the hydraulic and biochemical processes in CWs. Currently, employed modeling approaches can be seen in two categories, i.e. "black-box models" and "process-based models". It is evident that future development in wetland technology will depend on improved scientific knowledge of internal treatment mechanisms.

A promising approach of reject water treatment using a tidal flow constructed wetland system employing alum sludge as main substrate

This study examined a novel reuse of alum sludge, an inescapable by-product of drinking water treatment process when aluminium salt is added as a coagulant, as the main medium in a laboratory-scale multi-stage constructed wetland (CW) system for reject water treatment. Such reject water is a main concern in municipal wastewater treatment plant (MWWTP) for increasing the organic and nutrient loading. A 'tidal flow' strategy was employed to enhance the wetland aeration to stimulate organic matters (OM) and ammoniacal-nitrogen (N) oxidation while the 'step feed' operation was adopted to supply the necessary amount of carbon source for denitrification. The results reveal that alum sludge acting as P adsorbent can secure the P removal. Meanwhile, high removals of N and OM can also be obtained due to the active bacteria growth on the alum sludge surface. The results show that average removal efficiencies of 65.4 +/- 12.3% for chemical oxygen demand (COD), 67.8 +/- 9.2% for five-day biochemical oxygen demand (BOD5), 33.6 +/- 17.0% for N and 99.5 +/- 0.49% for P can be achieved over a period of 190 days. This indicates that novel reuse of alum sludge as medium in CW system can provide a promising approach for reject water treatment. Therefore, it will significantly reduce the amount of pollutant feedback through reject water recycling in a MWWTP.

Towards the development of a novel construction solid waste (CSW) based constructed wetland system for tertiary treatment of secondary sewage effluents

This study was conducted to examine the possibility of using construction solid waste (CSW), an inevitable by-product of the construction and demolition process, as the main substrate in a laboratory scale multi-stage constructed wetland system (CWs) to improve phosphorus (P) removal from secondary sewage effluent. A tidal-flow operation strategy was employed to enhance the wetland aeration. This will stimulate aerobic biological processes and benefit the organic pollutants decomposition and nitrification process for ammoniacal-nitrogen (NH(+)(4)-N) removal. The results showed that the average P concentration in the secondary sewage effluent was reduced from 1.90 mg-P/L to 0.04 mg-P/L. CSW presents excellent P removal performance. The average NH(+)(4)-N concentration was reduced from 9.94 mg-N/L to 1.0 mg-N/L through nitrification in the system. The concentration of resultant nitrite and nitrate in the effluent of the CSW based CWs ranged from 0.1 to 2.4 mg-N/L and 0.01 to 0.8 mg-N/L, respectively. The outcome of this study has shown that CSW can be successfully used to act as main substrate in CWs. The application of CSW based CWs on improving N and P removals from secondary sewage effluent presents a win-win scenario. Such the reuse of CSW will benefit both the CSW disposal and nutrient control from wastewater. More significantly, such the application can transfer the CSW from a 'waste' to 'useful' material and can ease the pressure of construction waste solid management. Meanwhile, the final effluent from the CSW-based CWs can be used as non-potable water source in landscape irrigation, agriculture and industrial process.

Diurnal fluctuations in oxygen release from roots of Acorus calamus Linn in a modeled constructed wetland

Oxygen is known to be released from plant roots, but has seldom been quantified for wetland plants. Our study aims to quantify oxygen release from the roots of one wetland species in China, and use this knowledge as a basis for future modeling. We measured diurnal fluctuations in oxygen release from the roots of Acorus calamus Linn in a modeled constructed wetland (CW) using a titanium ([image omitted]) citrate buffer. Oxygen release was monitored every two hours. Maximum oxygen release was recorded in the range of 215.2-750.8 μmolg(-1)h(-1) and occurred around 15:00. The maximum value of photosynthetically active radiation (PAR) was in the range of 1281.8-1712.0 mmolm(-2)s(-1) and occurred around 13:00. Both the oxygen release rate and PAR were found to approach zero at night. Our results indicate that oxygen release depends largely on light intensity and exhibits a diurnal periodicity with release occurring only during daytime. Rate of root oxygen release varied during the daytime and this temporal variation was well described by the Gaussian function. While further validation is needed, we suggest that the Gaussian function may be used as the basis for modeling root oxygen release in natural and constructed wetlands.

Process-based modelling of phosphorus removal in a novel constructed wetland system using dewatered alum-sludge as substrate

A process-based model that can evaluate the transport and the fate of phosphorus (P) in agricultural wastewater was developed for a novel 4-stage dewatered alum sludge cakes (DASC) based constructed wetlands (CWs) system using STELLA software (version 9.1.4). The model considered adsorption, plant and microbial uptakes as the major forms of P involved in the transformation chains. The results were obtained by experimental procedure through laboratory measurement, from literature and/or calibration. The observed effluent P concentration in the CWs ranged from 3.62 to 8.50 mg/L (stage 1), 2.00 to 4.45 mg/L (stage 2), 1.39 to 3.76 mg/L (stage 3) and 0.52 to 2.36 mg/L (stage 4), whereas the simulated values ranged from 2.12 to 10.99 mg/L (stage 1), 1.32 to 5.65 mg/L (stage 2), 0.84 to 3.64 mg/L (stage 3) and 0.53 to 2.25 mg/L (stage 4), respectively. The simulated and observed values of P removal in the CWs system were in good agreement. A mass balance analysis was performed for all the major processes which resulted in a major pathway of P removal through adsorption (64-75%, 58-66%, 57-63% and 49-58%) followed by plant uptake (7-11%, 8-14%, 14-17% and 9-19%) and microbial uptake (3-7%, 3-5%, 9-12% and 7-12%) for stage 1, stage 2, stage 3 and stage 4, respectively. Thus the mathematical model developed in this study could be used to explain the removal processes and simulate the fate of P in the DASC-based CWS system.

On the fit of statistical and the k-C* models to projecting treatment performance in a constructed wetland system

The objective of this study was to assess the suitability of statistical and the k-C* models to projecting treatment performance of constructed wetlands by applying the models to predict the final effluent concentrations of a pilot field-scale constructed wetlands system (CWs) treating animal farm wastewater. The CWs achieved removal rates (in g/m(2).d) ranging from 7.1-149.8 for BOD(5), 49.8-253.8 for COD and 7.1-47.0 for NH(4)-N. Generally, it was found that the statistical models developed from multiple regression analyses (MRA) were stronger in predicting final effluent concentrations than the k-C* model. However, both models were inadequate in predicting the final effluent concentrations of NO(3)-N. The first-order area-based removal rate constants (k, m/yr) determined from the experimental data were 200.5 for BOD(5), 80.1 for TP and 173.8 for NH(4)-N and these indicate a high rate of pollutant removal within the CWs.

STELLA software as a tool for modelling phosphorus removal in a constructed wetland employing dewatered alum sludge as main substrate

A dynamic simulation model was developed for the removal of soluble reactive phosphorus (SRP) from the vertical flow constructed wetlands (VFCW) using a dynamic software program called STELLA (structural thinking, experiential learning laboratory with animation) 9.1.3 to aid in simulating the environmental nature and succession of relationship between interdependent components and processes in the VFCW system. In particular, the VFCW employed dewatered alum sludge as its main substrate to enhance phosphorus (P) immobilization. Although computer modelling of P in treatment wetland has been well studied especially in recent years, there is still a need to develop simple and realistic models that can be used for investigating the dynamics of SRP in VFCWs. The state variables included in the model are dissolved phosphorus (DISP), plant phosphorus (PLAP), detritus phosphorus (DETP), plant biomass (PLBI) and adsorbed phosphorus (ADSP). The major P transformation processes considered in this study were adsorption, plant and microbial uptake and decomposition. The forcing functions which were considered in the model are temperature, radiation, volume of wastewater, P concentration, contact time, flow rate and the adsorbent (i.e., alum sludge). The model results revealed that up to 72% of the SRP can be removed through adsorption process whereas the uptake by plants is about 20% and the remaining processes such as microbial P utilization and decomposition, accounted for 7% SRP removal based on the mass balance calculations. The results obtained indicate that the model can be used to simulate outflow SRP concentration, and it can also be used to estimate the amount of P removed by individual processes in the VFCW using alum-sludge as a substrate.

Application of constructed wetland for urban lake water purification: trial of Xing-qing Lake in Xi'an city, China

A comprehensive review of the current water pollution status in China has indicated that the urban lakes in Chinese cities have suffered from serious pollution and are in high risk of eutrophication, although the pollution sources have been largely controlled. The objective of this study lies in exploring a long term restoration of the aquatic ecosystem in Chinese city lakes using treatment wetland, an environmentally friendly and cost-effective technology. Trials from a subsurface horizontal flow constructed wetland (CW) have demonstrated that the treatment wetland can be used for a purpose such as lake water quality control. Average removal of 84.2% for COD, 53.8% for NH(3)-N, 47.9% for TN, 73.3% for TP and 86.6% for SS can be achieved. Relatively, low removal of nitrogen lies in the lack of nitrification and denitrification process. Accordingly, improved configuration of the treatment wetland system has been proposed and discussed. Finally, the importance of the integrated constructed wetland especially for the application of urban lake water treatment is highlighted.

Equilibrium and kinetic analysis of phosphorus adsorption from aqueous solution using waste alum sludge

Excess phosphorus (P) in wastewaters promotes eutrophication in receiving waterways. A cost-effective method such as use of novel low-cost adsorbents for its adsorptive removal would significantly reduce such impacts. Using batch experiments, the intrinsic dynamics of P adsorption by waste alum sludge (an inevitable by-product of drinking water treatment plants) was examined. Different models of adsorption were used to describe equilibrium and kinetic data, calculate rate constants and determine the adsorption capacity. Results indicate that the intraparticle rate constant increased from 0.0075 mg g(-1)min(-1) at 5 mg L(-1) to 0.1795 mg g(-1)min(-1) at 60 mg L(-1) indicating that more phosphate is adsorbed per g min at higher P concentration. Further analyses indicate involvement of film and particle diffusion mechanisms as rate controlling steps at lower and higher concentrations, respectively. Mass transfer coefficient obtained ranged from 1.7 × 10(-6) to 1.8 × 10(-8) indicating a rapid transportation of phosphate molecules onto the alum sludge. These results further demonstrates that alum sludge-hitherto thought of as undesirable waste, can be used as novel adsorbent for P removal from wastewater through various applications, thus offsetting a portion of the disposal costs while at the same time improving water quality in sensitive watersheds.

Two strategies for improving animal farm wastewater treatment in reed beds

In this study, dewatered alum sludge cakes were used as substrate in a laboratory scale tidal vertical flow reed bed system treating animal farm wastewater. Tidal flow operation was employed to enhance oxygen transfer into the system while dewatered alum sludge cake was used to enhance phosphorus (P) removal through ligand exchange. Except for the removal of P which was consistently high throughout the experiment, the removal of organics (BOD5, COD) exhibited a trend of gradual and increasing removal and this highlights the benefits of using dewatered alum sludge cake in the reed bed. For the removal of organics, a mean removal percentage of 82.3 +/- 3.5% was obtained for BOD5 at a mean loading rate of 84.6 g/m2.d. The first-order kinetics constant for BOD5 removal (K(BOD), m/d) obtained was about 9 times the rate constant commonly obtained in conventional horizontal flow systems. The mean level of dissolved aluminium (Al) monitored in the effluent was 0.04 +/- 0.01 mg/1 and this is well below the discharge limit of 0.2 mg/l for Al discharge into all waters.

Leachability and leaching patterns from aluminium-based water treatment residual used as media in laboratory-scale engineered wetlands

CONCEPT AND PURPOSE: Virtually all water treatment facilities worldwide generate an enormous amount of water treatment residual (WTR) solids for which environmentally friendly end-use options are continually being sought as opposed to their landfilling. Aluminium-based WTR (Al-WTR) can offer huge benefits particularly for phosphorus (P) removal and biofilm attachment when used as media in engineered wetlands. However, potential environmental risks that may arise from the leaching out of its constituents must be properly evaluated before such reuse can be assured. This paper presents results of an assessment carried out to monitor and examine the leachability and leaching patterns of the constituents of an Al-WTR used as media in laboratory-scale engineered wetland systems.

MAIN FEATURES, MATERIALS AND METHODS

Al-WTR was used as media in four different configurations of laboratory-scale engineered wetland systems treating agricultural wastewater. Selected metal levels were determined in the Al-WTR prior to being used while levels of total and dissolved concentration for the metals were monitored in the influent and effluent samples. The increase or decrease of these metals in the used Al-WTR and their potential for leaching were determined. Leached metal levels in the effluents were compared with relevant environmental quality standards to ascertain if they pose considerable risks.

RESULTS

Aluminium, arsenic, iron, lead and manganese were leached into the treated effluent, but aluminium exhibited the least leaching potential relative to its initial content in the fresh Al-WTR. Levels of P increased from 0.13 mg-P/g (fresh Al-WTR) to 33.9-40.6 mg-P/g (used Al-WTR). Dissolved levels of lead and arsenic (except on one instance) were below the prescribed limits for discharge. However, total and dissolved levels of aluminium were in most cases above the prescribed limits for discharge, especially at the beginning of the experiments.

CONCLUSIONS, RECOMMENDATIONS AND PERSPECTIVES

Overall, the study indicates that leaching is observed when Al-WTR is beneficially reused for enhanced P removal in engineered wetlands. In particular, levels of aluminium in the treated effluent beyond the prescribed limits of 0.2 mg/l were observed. However, since the results obtained indicate that aluminium leached is mostly associated with solids, a post-treatment unit which can further reduce the level of aluminium in the treated effluent by filtering out the solids could serve to mitigate this. In addition, plants used in such wetland systems can uptake metals and this can also be a potential solution to ameliorating such metal releases. Periodic monitoring is thus advised. Notwithstanding, the use of Al-WTR as a media in engineered wetlands can serve to greatly enhance the removal of P from wastewaters and also serve as support material for biofilm attachment.

Extending the use of dewatered alum sludge as a P-trapping material in effluent purification: Study on two separate water treatment sludges

The generation of alum sludge from drinking water purification process remains inevitable when aluminium sulphate is used as primary coagulant for raw water coagulation. Sustainable managing such the sludge becomes an increasing concern in water industry. Its beneficial reuse is therefore highly desirable and has attracted considerable research efforts. In view of the novel development of alum sludge as a value-added raw material for beneficial reuse for wastewater treatment, this study examined the maximum phosphorus-adsorption capacity of two dewatered alum sludges sampled from two largest water treatment works in Dublin, Ireland. The objective lies in clarifying the change of alum sludge characteristics and its P-adsorption capacity over the location of the alum sludge produced and the raw water being treated. Experiments have demonstrated that the two alum sludges have the similar P adsorption capacity (14.3 mg P/g sludge for Ballymore-Eustace sludge and 13.1 mg P/g sludge for Leixlip sludge at pH 7.0). However, the study supports that alum sludge beneficial reuse as a low cost adsorbent for P immobilization should study its P-adsorption capacity before any decision of large application is made since the raw water quality will affect the sludge characteristics and therefore influence its adsorption ability.

Alum sludge-based constructed wetland system for enhanced removal of P and OM from wastewater: concept, design and performance analysis

The concept, design and performance analysis of a four-stage novel constructed wetland system (CWs) capable of enhanced and simultaneous removal of phosphorus (P) and organic matter (OM) from wastewaters is described. Alum sludge, a largely available by-product of drinking water facilities using aluminium salts as coagulant was used as the media. Under a hydraulic loading rate of 1.27 m(3)/m(2) d and a range of organic loading rate of 279.4-774.7 g-BOD(5)/m(2)d and 361.1-1028.7 g-COD/m(2)d, average removal efficiencies (mean+/-SD) of 90.6+/-7.5% for BOD(5) and 71.8+/-10.2% for COD were achieved, respectively. P removal was exceptional with average removal efficiency of 97.6+/-1.9% achieved for soluble reactive P at a mean influent concentration of 21.0+/-2.9 mg/l. Overall, the system holds great promise as a novel CWs for simultaneous removal of P and OM, and at the same time, it transforms alum sludge from a waste into a useful material.

Decolouration of H2SO4 leachate from phosphorus-saturated alum sludge using H2O2 and advanced oxidation processes in phosphorus recovery strategy

As a part of attempt for phosphorus (P) recovery from P-saturated alum sludge, which was used as a low-cost P-adsorbent in treatment reed bed for wastewater treatment, decolouration of H(2)SO(4) leachate obtained from previous experiment, possessing a great deal of P, aluminum and red-brown coloured materials (RBCMs), by using H(2)O(2) and advanced oxidation processes (AOPs) was investigated. The use of H(2)O(2) and AOPs in the forms of Fenton (H(2)O(2)/Fe(2 +)) and photo-Fenton (UV/H(2)O(2)/Fe(2 +)) were tested. The changes in colour and total organic carbon (TOC) were taken place as a result of mineralization of RBCMs. The results revealed that all of these three processes examined were efficient. It was found that about 98% colour and 47% TOC can be removed under photo-Fenton treatment after 8 hours of UV irradiation.Correspondingly, the reaction rates of H(2)O(2) and Fenton systems were slow, but 100% colour and 59% TOC removal of H(2)O(2) process and 100% colour and 67% TOC reductions of Fenton process can be achieved after 72 hours of reaction. The changes of structure and molecular weight/size of RBCMs were also evaluated by HPLC and UV-vis spectroscopic analysis. From the results, some chromophores of RBCMs such as aromatic groups were appeared to be easily degraded to the smaller refractory components. Hence, based on the experimental results and considering the investment and expediency of operation, H(2)O(2) and Fenton oxidation could be suitable technologies for the treatment of the RBCMs derived from P-extraction stage by using H(2)SO(4) leaching.

Characterization of aluminium-based water treatment residual for potential phosphorus removal in engineered wetlands

Aluminium-based water treatment residual (Al-WTR) is the most widely generated residual from water treatment facilities worldwide. It is regarded as a by-product of no reuse potential and landfilled. This study assessed Al-WTR as potential phosphate-removing substrate in engineered wetlands. Results indicate specific surface area ranged from 28.0 m(2) g(-1) to 41.4 m(2) g(-1). X-ray Diffraction, Fourier transform infrared and energy-dispersive X-ray spectroscopes all indicate Al-WTR is mainly composed of amorphous aluminium which influences its phosphorus (P) adsorption capacity. The pH and electrical conductivity ranged from 5.9 to 6.0 and 0.104 dS m(-1) to 0.140 dS m(-1) respectively, showing that it should support plant growth. Batch tests showed adsorption maxima of 31.9 mg P g(-1) and significant P removal was achieved in column tests. Overall, results showed that Al-WTR can be used for P removal in engineered wetlands and it carries the benefits of reuse of a by-product that promotes sustainability.

Development of alum sludge-based constructed wetland: an innovative and cost effective system for wastewater treatment

This article describes a research attempt to integrate the dewatered alum sludge, a residual by-product of drinking water treatment process, into a constructed wetland (CW) system for the purpose of enhancing the wastewater treatment performance, thus developing a so called alum sludge-based constructed wetland system. A multi-dimensional research project including the batch tests of phosphorus (P) adsorption onto alum sludge followed by the model CWs trials of single and multi-stage CWs, has been conducted since 2004. It has been successfully demonstrated that the alum sludge-based CW is capable of enhanced and simultaneous removal of P and organic matter (in terms of BOD5 and COD), particularly from medium and high strength wastewater. The sludge cakes act as the carrier for developing biofilm for organics removal and also serve as adsorbent to enhance P immobilization. Batch P-adsorption tests revealed that the alum sludge tested possesses excellent P-adsorption ability of 14.3 mg-P/g x sludge (in dry solids) at pH 7.0 with the adsorption favored at lower pH. The results obtained in a 4-stage treatment wetland system suggest that high removal efficiencies of 90.4% for COD, 88.0% for BOD5, 90.6% for SS, 76.5% for TN and 91.9% for PO4(3-)-P under hydraulic loading of 0.36 m3/m2 x d can be achieved. The field demonstration study of this pioneering development is now underway.

Evaluating the photo-catalytic application of Fenton's reagent augmented with TiO(2) and ZnO for the mineralization of an oil-water emulsion

In the present study, homogenous (photo-Fenton) and heterogeneous photo-assisted systems (Fenton/TiO(2)/UV, Fenton/ZnO/UV and Fenton/TiO(2)/UV/Air) were investigated for the treatment of a diesel-oil wastewater emulsion. The augmentation of the photo-Fenton process by heterogeneous TiO(2) increased the reaction rate, in terms of COD reduction efficiency from 61% to 71%. Furthermore, the COD removal efficiency was increased to 84% when air was bubbled through the reactants. However, if the Fenton/TiO(2) /UV/Air process is to be utilized as a treatment for this wastewater, the separation of the TiO(2) from the treated effluent would need further consideration.