Activated Sludge Plant Research Articles

Estimating Biodiversity of Fungi in Activated Sludge Communities Using Culture-Independent Methods

Fungal diversity of communities in several activated sludge plants treating different influent wastes was determined by comparative sequence analyses of their 18S rRNA genes. Methods for DNA extraction and choice of primers for PCR amplification were both optimised using denaturing gradient gel electrophoresis profile patterns. Phylogenetic analysis revealed that the levels of fungal biodiversity in some communities, like those treating paper pulp wastes, were low, and most of the fungi detected in all communities examined were novel uncultured representatives of the major fungal subdivisions, in particular, the newly described clade Cryptomycota. The fungal populations in activated sludge revealed by these culture-independent methods were markedly different to those based on culture-dependent data. Members of the genera Penicillium, Cladosporium, Aspergillus and Mucor, which have been commonly identified in mixed liquor, were not identified in any of these plant communities. Non-fungal eukaryotic 18S rRNA genes were also amplified with the primer sets used. This is the first report where culture-independent methods have been applied to flocculated activated sludge biomass samples to estimate fungal community composition and, as expected, the data obtained gave a markedly different view of their population biodiversity compared to that based on culture-dependent methods.

N2O Emissions: Modeling the Effect of Process Configuration and Diurnal Loading Patterns

The objective of this research was to develop a mechanistic model for quantifying N2O emissions from activated sludge plants and demonstrate how this may be used to evaluate the effects of process configuration and diurnal loading patterns. The model describes the mechanistic link between the factors recognized to correlate positively with N2O emissions. The primary factors are the presence of ammonia and nitrite accumulation. Low dissolved oxygen concentrations also may be implicated through differential impacts on ammonia-oxidizing bacteria (AOB) versus nitrite-oxidizing bacteria (NOB) activity. Factors promoting N2O emissions at treatment plants are discussed below. The model was applied to data from laboratory and pilot-scale systems. From a practical standpoint, plant configuration (e.g., plug-flow versus complete-mix), influent loading patterns (and peak load), and certain operating strategies (e.g., handling of return streams) are all important in determining N2O emissions.

Distribution and mass balance of hexavalent and trivalent chromium in a subsurface, horizontal flow (SF-h) constructed wetland operating as post-treatment of textile wastewater for water reuse

In this study, during a two-year period, we investigated the fate of hexavalent and trivalent chromium in a full-scale subsurface horizontal flow constructed wetland planted with Phragmites australis. The reed bed operated as post-treatment of the effluent wastewater from an activated sludge plant serving the textile industrial district and the city of Prato (Italy). Chromium speciation was performed in influent and effluent wastewater and in water-suspended solids, at different depths and distances from the inlet; plants were also analyzed for total chromium along the same longitudinal profile. Removals of hexavalent and trivalent chromium equal to 72% and 26%, respectively were achieved. The mean hexavalent chromium outlet concentration was 1.6 ± 0.9 μg l −1 and complied with the Italian legal limits for water reuse. Chromium in water-suspended solids was in the trivalent form, thus indicating that its removal from wastewater was obtained by the reduction of hexavalent chromium to the trivalent form, followed by accumulation of the latter inside the reed bed. Chromium in water-suspended solids was significantly affected by the distance from the inlet. Chromium concentrations in the different plant organs followed the same trend of suspended solids along the longitudinal profile and were much lower than those found in the solid material, evidencing a low metal accumulation in P. australis.

A review of the impact and potential of intermittent aeration on continuous flow nitrifying activated sludge

Intermittent aeration of activated sludge plants (ASPs) is a potential strategy that may help deliver reduced operational costs while providing an adequate effluent quality. This review paper critically assesses the implications of temporary turning aeration off in continuous flow nitrifying ASPs, including impact on dissolved oxygen concentrations, process biology and operational parameters. The potential savings and pitfalls of the approach are further illustrated through an example scenario. Findings from this review indicate rapid dissolved oxygen depletion times of 1–60 minutes and a significant reduction of nitrification rates from 0.12 to less than 0.04 g NH4-N/g VSS/d. Further negative impacts include a potential increase in nitrous oxide emissions from 0.07% to 27% N2O-N per mole of NH4-N oxidized; enhanced filamentous bacteria growth; a noticeable increase in effluent turbidity developing within one hour of air supply interruption; and, if no mechanical mixing is in place, risk of mixed liquor suspended solids settling in the bioreactor within short times (23–53 min). However, the potential savings in terms of aeration costs could amount to 33%–45% if instrumentation adequacy and impact on process biology and carbon equivalent emissions are excluded from the economic analysis. Further research on the areas of nitrous oxide emissions and the use of hybrid systems to provide resilience and robustness to the intermittent operation of continuous flow nitrifying ASPs is recommended.

Small but Sufficient: the Rhodococcus Phage RRH1 Has the Smallest Known Siphoviridae Genome at 14.2 Kilobases

Bacteriophages are considered to be the most abundant biological entities on the planet. The Siphoviridae are the most commonly encountered tailed phages and contain double-stranded DNA with an average genome size of ∼50 kb. This paper describes the isolation from four different activated sludge plants of the phage RRH1, which is polyvalent, lysing five Rhodococcus species. It has a capsid diameter of only ∼43 nm. Whole-genome sequencing of RRH1 revealed a novel circularly permuted DNA sequence (14,270 bp) carrying 20 putative open reading frames. The genome has a modular arrangement, as reported for those of most Siphoviridae phages, but appears to encode only structural proteins and carry a single lysis gene. All genes are transcribed in the same direction. RRH1 has the smallest genome yet of any described functional Siphoviridae phage. We demonstrate that lytic phage can be recovered from transforming naked DNA into its host bacterium, thus making it a potentially useful model for studying gene function in phages.

Upgrading activated sludge systems and reduction in excess sludge

Most of 200 Activated Sludge Plant in Iran are overloaded and as a result, their efficiency is low. In this work, a pilot plant is manufactured and put into operation in one of the wastewater treatment plants in the west of Tehran. Instead of conventional activated sludge, a membrane bioreactor and an upflow anaerobic sludge blanket reactor used as a pretreatment unit in this pilot. For the sake of data accuracy and precision, an enriched municipal wastewater was opted as an influent to the pilot. Based on the attained result, the optimum retention time in this system was 4h, and the overall COD removal efficiency was 98%. As a whole, the application of this retrofit would increase the plant’s capacity by a factor of 5 and reducing the excess sludge by a factor of 10. The sludge volume index in the anaerobic reactor was about 12 after granulation occurred.

The application of model predictive control of ammonia nitrogen in an activated sludge process

In this paper a model predictive controller (MPC) for ammonia nitrogen is presented and evaluated in a real activated sludge process. A reduced nonlinear mathematical model based on mass balances is used to model the ammonia nitrogen in the activated sludge plant. An MPC algorithm that minimises only the control error at the end of the prediction interval is applied. The results of the ammonia MPC were compared with the results of the ammonia feedforward-PI and ammonia PI controllers from our previous study. The ammonia MPC and ammonia feedforward-PI controller give better results in terms of ammonia removal and aeration energy consumption than the ammonia PI controller because of the measurable disturbances used. On the other hand, with the ammonia MPC, comparable or even slightly poorer results than with the ammonia feedforward-PI controller are obtained. Further improvements to the MPC could be possible with an improved accuracy of the nonlinear reduced model of the ammonia nitrogen, more sophisticated control criteria used inside the controller and the extension of the problem from univariable ammonia to multivariable total nitrogen control.

Total and hexavalent chromium removal in a subsurface horizontal flow (h-SSF) constructed wetland operating as post-treatment of textile wastewater for water reuse

In this study we investigated total and hexavalent chromium removal in an h-SSF constructed wetland (CW) planted with Phragmites australis and operating as post-treatment of effluent wastewater from an activated sludge plant serving the textile industrial district of Prato (Italy). Two measurement campaigns were carried out in 2006 and 2008-2010 in which more than 950 inlet and outlet samples were analyzed. When inlet and outlet concentrations were compared one to the other, the latter were found to be significantly lower than the former (p < 0.001); during the entire period of investigation, removal of hexavalent chromium equal to about 70% was achieved. Outlet concentrations ranged between values lower than the quantification limit (0.5 microg L(-1)) and 4.5 microg L(-1), and in all cases were therefore lower than the limit indicated for hexavalent chromium in the Italian regulation for water reuse (5 microg L(-1)). The comparison of the removal efficiencies achieved for hexavalent and trivalent chromium during the two campaigns suggested that the removal of the former can be sustained in the long term, while for the latter, the treatment efficiency is more sensitive to the age of the CW, being that it is it based on trivalent chromium retention in the reed bed.

Assessing the diurnal variability of pharmaceutical and personal care products in a full-scale activated sludge plant

An intensive sampling campaign has been carried out in a municipal wastewater treatment plant (WWTP) to assess the dynamics of the influent pharmaceutical active compounds (PhAC) and musks. The mass loadings of these compounds in wastewater influents displayed contrasting diurnal variations depending on the compound. The musks and some groups of PhACs tended to follow a similar diurnal trend as compared to macropollutants, while the majority of PhACs followed either the opposite trend or no repeatable trend. The total musk loading to the WWTP was 0.74±0.25gd−1, whereas the total PhAC mass loading was 84.7±63.8gd−1. Unlike the PhACs, the musks displayed a high repeatability from one sampling day to the next. The range of PhAC loadings in the influent to WWTPs can vary several orders of magnitude from one day or week to the next, representing a challenge in obtaining data for steady-state modelling purposes.

ChemInform Abstract: Recalcitrant Industrial Wastewater Treatment by Membrane Bioreactor (MBR)

AbstractReview: 125 refs.

Assessment of diffuser pressure loss on WWTPs in Baden-Württemberg

Aeration of activated sludge is a critical treatment step for the operation of activated sludge plants. To achieve a cost effective treatment process, assessing and benchmarking of aeration system performance are important measures. A simple means of gauging the relative condition of a fine bubble diffused aeration system is to evaluate the pressure loss of the diffusers as oxygen transfer tests are rarely applied during the lifetime of an aeration system. This paper shows an assessment of fine bubble diffuser systems in Baden-Württemberg, Germany, based on the results of a questionnaire sent to 941 WWTPs. Apart from the results with regards to the diffuser pressure loss, this paper also presents information on the current state of diffuser technology such as types and materials as well as the diffuser cleaning methods used in Baden-Württemberg. The majority of the WWTPs were equipped with tube diffusers (71%) with 50% of all plants having EPDM membranes installed. Regular mechanical cleaning is the most common cleaning method followed by regular pressure release/air-bumping programs during operations. With regard to the diffuser pressure loss it was found that 50% of the evaluated plants had a diffuser pressure loss that was twice as high as measured for new diffusers.

Mycological survey of activated sludge in MBRs

The objective of this research was to conduct a survey of fungi in activated sludge plants with membrane bioreactors (MBRs). Thirty-six samples of both aerobic and anoxic activated sludge were taken from two plants with MBRs treating domestic wastewater. Over a period of 8 months, two samples from each plant were taken per month. The samples were prepared for count and identification of fungi. The obtained data show that 61 species belonging to 30 genera were identified from activated sludge samples, under aerobic conditions (27 genera and 54 species) and anoxic conditions (21 genera and 39 species), by culturing at 30 °C for 15 days. In aerobic activated sludge samples, the prevalence of Geotrichum candidum was 100% followed by Fusarium (72.2%), yeast (61.1%), Aspergillus (50.0%), Penicillium (50.0%) and Trichoderma (41.6%), while in anoxic activated sludge, G. candidum (94.4%), Fusarium (91.6%), Aspergillus (77.7%), yeast (63.8%), Penicillium (50.0%) and Trichoderma (50.0%) species were the most prevalent. In addition, the other genera found included Chaetomum, Chrysosporium, Cladosporium, Doratomyces, Gibberella, Gliocladium, Gymnoascus, Mucor, Paecilomyces, Phialophora, Rhizopus, Scopulariopsis, Stachybotrys, Stemphylium and others. The results indicate that aerobic and anoxic activated sludge provides a suitable habitat for the growth and sporulation of different groups of fungi, both saprophytic and pathogenic.

Modelling and dynamic simulation of hybrid moving bed biofilm reactors: Model concepts and application to a pilot plant

In the recent years, there has been an increasing interest in the development of hybrid reactors, especially in the up-grading of existing activated sludge plants that are no longer able to comply with concentration limits established by regulatory agencies. In such systems the biomass grows both as suspended flocs and as biofilm. In this way, it is possible to obtain a higher biomass concentration in the reactor, but without any significant increase of the load to the final clarifier. The paper presents the setting-up of a dynamic mathematical model aimed at quantitatively describing the biokinetic processes occurring in a hybrid moving bed biofilm reactor (HMBBR), and, more in general, in integrated fixed-film activated sludge (IFAS) processes, as well as to compare the simulation results with measured data from a HMBBR pilot plant built at the Norwegian University of Science and Technology in Trondheim (Norway). Particularly, the pilot plant consisted of three aerobic tanks in series; the first and third aerobic reactors were pure suspended biomass systems, while the second aerobic reactor was filled with the AnoxKaldnes™ K1 carriers for biofilm development. The mathematical model consists of two connected models for the simulation of both suspended biomass and biofilm. Biochemical conversions are evaluated according to the well known matrix notation used in the Activated Sludge Model No. 1 (ASM1) for both attached and suspended biomass and, in addition to biochemical conversion, the model contains the simulation of particulate detachment from the biofilm into the bulk liquid. The results showed an overall good agreement between measured and simulated data, for both biofilm and suspended biomass, with a good reproduction of dynamic processes in the hybrid moving bed pilot plant, and they are encouraging for further developments.

An assessment of the fate, behaviour and environmental risk associated with sunscreen TiO 2 nanoparticles in UK field scenarios

The fate of Ti was examined in an activated sludge plant serving over 200,000 people. These studies revealed a decrease of 30 to 3.2 μg/L of Ti < 0.45 μm from influent to effluent and a calculated Ti presence of 305 mg/kg DW in wasted sludge. Thus, using sludge as a fertiliser would result in a predicted deposition of up to 250 mg/m 2 of Ti to soil surfaces using a recommended maximal agricultural application rate. Given the major use of TiO 2 in many industrial and domestic applications where loss to the sewer is possible, this measured Ti was presumed to have been largely TiO 2, a proportion of which will be nanoparticle sized. To assess the behaviour of engineered nanoparticle (ENP) TiO 2 in sewage and toxicology studies, Optisol (Oxonica Materials Ltd) and P25 (Evonik Industries AG), which are representative of forms used in sunscreen and cosmetic products, were used. These revealed a close association of TiO 2 ENPs with activated sludge. Using commercial information on consumption, and removal rates for sewage treatment, predictions were made for river water concentrations for sunscreen TiO 2 ENPs for the Anglian and Thames regions in Southern England. The highest predicted value from these exercises was 8.8 μg/L for the Thames region in which it was assumed that one in four people used the recommended application of sunscreen during a low flow (Q95) period. Ecotoxicological studies using potentially vulnerable species indicated that 1000 μg/L TiO 2 ENP did not affect the viability of a mixed community of river bacteria in the presence of UV light. Direct exposure to TiO 2 ENPs did not impair the immuno-effectiveness of earthworm coelomocyte cells at concentrations greatly above those predicted for sewage sludge.

Rapid quantification and analysis of genetic diversity among Gordonia populations in foaming activated sludge plants

Activated sludge plants, sporadically suffers malfunction due to the proliferation of filamentous bacteria mainly Gordonia and Microthrix species. Nested Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (nested PCR-RFLP) in combination with quantitative real-time PCR (q PCR) was applied to study the distribution of Gordonia in foaming samples. Samples of mixed liquor were collected from three full-scale activated sludge plants that were experiencing filamentous biological foaming. Partial sequencing of 16S rRNA genes revealed the dominance of Gordonia amarae (60-80%), Gordonia terrae (10%), Gordonia polyisoprenivorans (30-40%) and an unidentified Gordonia species (20-50%). Restriction enzyme analysis of the amplicons exhibited 87.14 to 99.6% similarity at interspecies level. The q PCR results showed that there was an average of 15.6% Gordonia 16S rRNA copies with respect to the total bacterial 16S rRNA gene in foaming sludge samples with the highest being 23.51% and lowest being 10.28%. The presence of Gordonia spp. in the foaming samples was observed throughout the year but was lower during winter and its presence was significantly higher in foaming samples, compared to Microthrix parvicella (r = 0.007, P < 5%). This approach could help to quantify and confirm the existence of genetically diverse indigenous Gordonia spp. in foaming samples and can be used as an indicator of forthcoming foaming incidents.

The activated sludge bulking filament Eikelboom morphotype 0914 is a member of the Chloroflexi

The filamentous bacterium Eikelboom morphotype type 0914 responsible for bulking in activated sludge plants is identified here for the first time as a member of the phylum Chloroflexi subgroup 1. Two FISH probes, CFX67a and CFX67b, targeting the 16S rRNA sequences of this filament morphotype were designed, validated and used successfully for its in situ identification. A survey of plants in eastern Australia with the CFX67a probe showed it targeted only the type 0914 morphotype that was common especially in long sludge age plants designed to remove phosphorus and nitrogen microbiologically, although being in very low abundance in many samples. Filaments responding to the CFX67b probe also exhibited the type 0914 morphology but were less frequent, although again occurring in similarly configured plants. All these filaments showed an uneven FISH signal suggesting their ribosomes are localized at the ends of their cells. Furthermore, some generated distinctive FISH signals in all biomass samples containing them, where only certain cells within any single trichome fluoresced with probes designed against different target sites. Helper probes for each of these were required before all cells fluoresced above the visual detection limits of FISH.

The fate and behavior of selected endocrine disrupting chemicals in full scale wastewater and sludge treatment unit processes

Endocrine disrupting chemicals are discharged into the environment mainly through wastewater treatment processes. There is a need for better understanding of the fate of these compounds in the unit processes of treatment plant to optimise their removal. The fate of oestrone, 17β-estradiol, 17α-ethinyestradiol and nonylphenol in the unit processes of full scale wastewater treatment plants in the UK, including activated sludge plant, oxidation ditch, biofilter and rotating biological contactor were investigated. The overall removal efficiencies of all the compounds ranged from 41 %to 100%. The removals were predominantly during the secondary biological treatment with the rates of removal related to the nitrification rates and the sludge age. The removal efficiency of the treatment processes were in the order activated sludge > oxidation ditch > biofilter > rotating biological contactors. Activated sludge plant configured for biological nutrient removal showed better removal of the endocrine disrupting chemicals compared to conventional activated sludge plant effluents. Tertiary treatment was also significant in the removal process through solids removal. Overall mechanisms of removal were biodegradation and sorption unto sludge biomass. Phytoremediation was also significant in the removal processes. The endocrine disrupting chemicals persisted in the anaerobic sludge digestion process with percentage removals ranging fro 10–48 %. Sorption of the endocrine disrupting chemicals onto the sludge increased with increasing values for the partitioning coefficients and the organic carbon contents of the sludge.

Hybrid activated sludge/biofilm process for the treatment of municipal wastewater in a cold climate region: a case study

A hybrid activated sludge/biofilm process was investigated for wastewater treatment in a cold climate region. This process, which contains both suspended biomass and biofilm, usually referred as IFAS process, is created by introducing plastic elements as biofilm carrier media into a conventional activated sludge reactor. In the present study, a hybrid process, composed of an activated sludge and a moving bed biofilm reactor was used. The aim of this paper has been to investigate the performances of a hybrid process, and in particular to gain insight the nitrification process, when operated at relatively low MLSS SRT and low temperatures. The results of a pilot-scale study carried out at the Department of Hydraulic and Environmental Engineering at the Norwegian University of Science and Technology in Trondheim are presented. The experimental campaign was divided into two periods. The pilot plant was first operated with a constant HRT of 4.5 hours, while in the second period the influent flow was increased so that HRT was 3.5 hours. The average temperature was near 11.5°C in the overall experimental campaign. The average mixed liquor SRT was 5.7 days. Batch tests on both carriers and suspended biomass were performed in order to evaluate the nitrification rate of the two different biomasses. The results demonstrated that this kind of reactor can efficiently be used for the upgrading of conventional activated sludge plant for achieving year-round nitrification, also in presence of low temperatures, and without the need of additional volumes.

Endocrine disrupting compounds: A comparison of removal between conventional activated sludge and membrane bioreactors

The removal of endocrine disrupting compounds (EDCs) was investigated in a conventional activated sludge plant connected with a tertiary treatment (CAS-TT) and two membrane bioreactor pilot plants installed with flat sheet (MBR-FS) and hollow fibre (MBR-HF) modules. Chemical compounds such as alkylphenols (4OP and 4tOP), nonylphenols (NP), bisphenol A (BPA), phthalates (DMP, DEP, DBP, BBP, BEHP, and DOP) and estrogens (E1 and EE2) were determined in dissolved wastewater by employing stir bar sorptive extraction and thermal desorption–gas chromatography–mass spectrometry. Samples were taken during three months from the outlet of the primary settling tank (PS), the tertiary treatment and the flat sheet and hollow fibre modules. All the target compounds were detected in the effluent of the PS during the monitored period except DMP, 4OP, DOP and EE2. The MBR modules were more efficient in the removal of DEP, DBP and BBP than CAS-TT, whereas CAS-TT was more efficient in the removal of BEHP. For 4tOP and BPA the removal efficiency found was very similar when CAS-TT or MBR treatments were applied. Only slight differences were detected comparing both MBR modules. MBR-HF seemed to be adequate for DBP and NP removal, while MBR-FS was better for DEP and BBP removal.

Low-carbon assessment for ecological wastewater treatment by a constructed wetland in Beijing

Presented in this paper is a low-carbon assessment for wastewater treatment by a constructed wetland as ecological engineering. Systems accounting by combining process and input–output analyses is applied to track both direct and indirect GHG emissions associated with the wastewater treatment. Based on the detailed assessment procedures and the embodied GHG emission intensity database for the Chinese economy in 2007, the GHG emissions embodied in both the construction and operation stages of a pilot constructed wetland in Beijing are investigated in concrete detail, with parallel calculations carried out for a cyclic activated sludge plant as a typical conventional wastewater treatment system for comparison. With the overall embodied GHG emissions taken into account, the constructed wetland is shown to be remarkably less carbon intensive than the conventional wastewater treatment system, and the contrast in GHG emission structure is also revealed and characterized. According to the results, the ecological engineering of the constructed wetland is considered to be favorable for achieving the low-carbon goal.