Wastewater Treatment Tank Research Articles

Performance evaluation and application of host-specific Bacteroidales and mitochondrial DNA markers to identify sources of fecal contamination in river water in Japan

Microbial source tracking (MST) using host-specific Bacteroidales and mitochondrial DNA (mtDNA) markers is an efficient tool to identify the sources of fecal contamination in environmental water. This study evaluated and updated the previously reported performances of seven host-specific Bacteroidales markers (three human-, two cattle-, and two pig-specific). Additionally, the performance of a cattle-specific Bovine mtDNA and a pig-specific Swine mtDNA marker were evaluated and then applied to MST of river water samples collected in Yamanashi Prefecture, Japan. We collected 48 fecal-source samples, including raw sewage, secondary-treated sewage, an effluent of a domestic wastewater treatment tank, pig feces, pig wastewater, and cattle feces, which were quantitatively analyzed using host-specific Bacteroidales and mtDNA markers. BacHum and gyrB markers (human-specific), BacR and Bovine mtDNA markers (cattle-specific), and Pig2Bac and Swine mtDNA markers (pig-specific) were judged the best-performing markers. Then, these selected markers were applied to MST to identify the sources of fecal contamination in 59 river water samples collected at 21 sites. Of them, 20 (95%), 21 (100%), and 16 (76%) sites were positive for at least one human, cattle, and pig marker, respectively, indicating the need for immediate action and monitoring to control fecal pollution.

Perencanaan dan penghitungan pengolahan limbah tahu di Pabrik Tahu Banggle, Jombang

Background: The soybean processing industry into tofu has environmental impacts. This industry generates waste in the form of wastewater, which if discharged without prior management will cause damage and pollution to the environment. One of them is the Banggle tofu factory in Jombang. This study aims to create a plan and calculation of wastewater treatment installations at the factory. Methods: The research method is laboratory testing to determine the quantity of wastewater and direct observation to determine field conditions so that appropriate plans can be made according to the field conditions. Finding: This study found that the largest wastewater discharge is 18,000 L/day or 18 m3/day. Therefore, pipes are buried underground to avoid leakage. This research also produces the sizes that must be met by the wastewater treatment tank as a result of calculations. Conclusion: These sizes need to be considered in the installation of wastewater treatment facilities.

Suitable technology for a household scale workshop systems for the treatment of wastewater

One of the causes of water pollution is the presence of workshop activities. Gasoline residue from washing spare parts and washing hands after repairing and maintaining motor vehicles can harm the surrounding environment, namely water pollution. This study aims to determine the efficiency of reducing the levels of pH, BOD, COD, TSS, oil and grease, Ammonia, and total coliform in wastewater from Astra workshop operations using three treatment and treatment units in the piping section and to determine the design of wastewater treatment tanks for operation astra workshop. Based on the preliminary test results, the waste from Astra workshop activities had a pH content of 7.2, a BOD content of 2.9 mg/l, a COD content of 58 mg/l, a TSS content of 2.45 mg/l, an oil and fat content of 8.702 mg/l, the ammonia content was 0.027 mg/l. The total coliform content was 2000 MPN/ml. Of these values, there is one parameter that does not meet the quality standards according to the Decree of the Minister of Environment and Forestry No. 68 of 2016 concerning Domestic Waste Quality Standards, namely a pH concentration of 6-9, a maximum level of BOD of 30 mg/l, a maximum level of COD of 100 mg/l, a maximum level of TSS of 30 mg/l, a maximum concentration of oils and fats allowed 5 mg/l, maximum ammonia concentration of 10 mg/l, and maximum permitted total coliform content of 3000 MPN/ml. This workshop liquid waste treatment uses three treatment and treatment units in the piping section with one filtration media, which is carried out in duplicate to anticipate and minimize the possibility of errors that can occur during the process. Efficiency in reducing parameters in liquid waste from Astra workshop operations using filtration media and treatment in the piping section can reduce the pH concentration by -15.29%, from an initial concentration of 7.2 to 8.5, TSS by 59.18% from an initial concentration of 2.45 mg/l to 1 mg /l. BOD was 72.41% from an initial concentration of 2.9 mg/l to 0.8 mg/l. COD was 65.51% from an initial concentration of 58 mg/l to 20 mg/l. Fatty oil was 45.41% from an initial concentration of 8,702 mg/l to 4.75 mg/l. Ammonia by 48.14% from the initial concentration of 0.027 mg/l to 0.014 mg/l, and Total Coliform by 100% from 2000 MPN/ml to 0 MPN/ml.

Wetland system for geothermal wastewater management

The SFS-Wetland model used is the wastewater treatment tank belonging to Pertamina Geothermal Lahendong. Based on the slope of the existing land, it is possible to design twin gravity wetlands of a certain size. This study aimed to develop a Surface Flow System Constructed Wetland design model using Monocaria vaginalis, Salvania molesta and Colocasia esculenta, analyze stakeholder perceptions of the SFS-Wetland Model, and refine this model based on stakeholder perceptions. Stakeholders' perception of the SFS-Wetland model based on a priority scale is that the geothermal waste management system is acceptable and accountable from an environmental perspective, waste management is socially and culturally acceptable, accountable and economically feasible. The components of the SFS-Wetland Model that must be improved are land availability, utilization of other local plant potentials, final geothermal wastewater temperature ranging from 33-35oC, ease of operation/maintenance, and low and environmentally friendly operational costs. The SFS-Wetland model suggested by stakeholders to improve is the existing SFS-Wetland model by taking into account the stakeholders' perceptions of the components that must be improved, namely the expansion of land for wetland ponds as much as 2x8 = 16 pool plots with a size of 35x60m = 33600 M2.

Integrated Life Cycle Assessment and Life Cycle Cost Assessment based fuzzy multi-criteria decision-making approach for selection of appropriate wastewater treatment system

The current study proposes a comprehensive fuzzy formulated Multi-Criteria Decision Making (MCDM) framework with integrated Life Cycle Assessment (LCA) and Life Cycle Cost Assessment (LCCA) approach for selection of best suitable wastewater treatment (WWT) system, especially for multi-storeyed residential buildings. By utilising a thorough literature survey, experts' opinions and questionnaires, the study attempts to identify four dimensions of sustainability with associated key nineteen indicators. Furthermore, the study is benefited by undertaking quantitative parameters related to environmental and economic sustainability assessed by LCA and LCCA respectively. The proposed three-phase methodological framework illustrates the identification of widely used WWT systems in the first phase followed by Fuzzy Analytic Hierarchy Process (FAHP) assessment for criteria and indicators' screening and finalisation in the second phase and ranking of alternative by Fuzzy Technique for Order of Preference by Similarity to Ideal Solution (FTOPSIS) in the third phase. Moreover, the current paper suggests a novel approach of incorporating “environmental floor” in multi-storeyed building, where gravity governed nature-based wastewater treatment tanks of Decentralized On-Site Integrated WAste Management (DOSIWAM) system can be positioned. To test the proposed framework, the sustainability of DOSIWAM system is compared with five widely used wastewater treatment systems viz. membrane bioreactor (MBR), moving bed biofilm reactor (MBBR), sequencing batch reactors (SBR), activated sludge process (ASP), soil biotechnology (SBT). Results of alternative ranking indicate DOSIWAM (allocated at environmental floors) as the best suitable option followed by the second, third and fourth rank of MBR, SBT and SBR respectively whereas, MBBR and ASP are the least preferred. It has been observed that the experts prefer mostly natural treatment systems since they are more sustainable in environmental and economic considerations. In addition, by changing the weights of the main criteria, sensitivity analysis is carried out considering five scenarios, which signifies in three out of five scenarios; relative percentage change in criteria weight does not affect the first rank of the DOSIWAM system. The developed framework successfully facilitates a reliable base for the selection of the best suitable WWT system for multi-storeyed residential building and could be made available to the relevant local planning authority to incentivize the effort undertaken for the welfare of citizens as well as the government.

Design Tables for Cylindrical Concrete Water Tank with Annular Footing

AbstractWater storage and wastewater treatment tanks are usually cylindrical in shape and made of reinforced cement concrete. These tanks are founded at the lowest hydraulic level to facilitate the...

Photocatalytic properties, mechanical strength and durability of TiO2/cement composites prepared by a spraying method for removal of organic pollutants

TiO2/cement composites were prepared by a spraying method to degrade organic pollutants. After coated with waterproof liquid, pure cement pastes/mortars were sprayed with TiO2 suspensions with different TiO2 contents and spraying times. Photocatalytic properties, mechanical strength and durability were studied. Maximum photocatalytic activity and uniform TiO2 distribution were achieved at the optimal conditions of 10 wt% TiO2 content in suspension and 3 spraying times. The TiO2/cement pastes had better degradation performance over Rhodamine B (RhB) and methylene blue (MB) than that over methyl orange (MO). After 20 times of cycling degradation, the photocatalytic efficiencies had no significant reduction. The TiO2/cement mortars had good mechanical strengths, meeting the mechanical demands of wastewater treatment tanks. In durability, the TiO2/cement mortars had better water penetration resistance, chloride penetration resistance and anti-carbonation than pure cement mortars.

Estimation of greenhouse gas emissions from solid waste management and wastewater treatment in the Nizam Zachman Fishery Port, Jakarta, Indonesia

Nizam Zachman is a modern fishery port located in Muara Baru, Jakarta, Indonesia. Some of its facilities include a temporary collection of solid waste and wastewater treatment plants, emitting greenhouse gases that lead us to climate change by warming up the global temperature. In this study, greenhouse gas emissions are estimated from these two facilities by using the IPCC Tier 1 method and emission factor calculation. By estimating greenhouse gas in this area, it will give knowledge and convicing to make greenport as a consideration of the strategy to reduce greenhouse gas emission, starting from waste and wastewater management. Solid waste treatment comprises open dumping, recycling, and transportation of wastes to the temporary landfill in this area. With a total waste of 5, 411.4 tons/year, greenhouse gas emissions from open dumping and transportation are estimated to be 14, 340.2 and 22.3 tons CO2eq/year, respectively. Meanwhile, recycling activities contribute to 143 tons CO2 eq/year of greenhouse gas emissions. In addition, the estimated greenhouse gas emissions include emissions from wastewater treatment, discharge of industrial wastewater to waterways via the drainage system, and domestic wastewater treatment by using a septic tank. In addition, greenhouse gas emissions from wastewater treatment, drainage system, and septic tanks are estimated to be 2, 830; 108.7; and 3.2 tons CO2 eq/year, respectively. Based on the estimation, solid waste treatment generates 83% of the total greenhouse gas emissions, while wastewater treatment generates only 17% of the total emissions. Herein, composting, increase of recycling, and utilization of methane are recommended to reduce the greenhouse gas emissions from waste management.

Contamination by Antibiotic-Resistant Bacteria in Selected Environments in Thailand.

This study determined the presence of important antibiotic-resistant bacteria in selected environments in Thailand, including wastewater samples from 60 hospitals; washed fluid, leachate, flies, cockroaches, and rats collected from five open markets; washed fluid from garbage trucks; and stabilized leachate from a landfill facility. At least one type of antibiotic-resistant bacteria was isolated from all samples of influent fluid before treatment in hospitals, from wastewater treatment tank content in hospitals, and from 15% of effluent fluid samples after treatment with chlorine prior to draining it into a public water source. Antibiotic-resistant bacteria were recovered from 80% of washed market fluid samples, 60% of market leachate samples, all fly samples, 80% of cockroach samples, and all samples of intestinal content of rats collected from the open markets. Antibiotic-resistant bacteria were recovered from all samples from the landfill. Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and/or Klebsiella pneumoniae were the most common antibiotic-resistant bacteria recovered from all types of samples, followed by carbapenem-resistant E. coli and/or K. pneumoniae. Colistin-resistant Enterobacteriaceae, carbapenem-resistant Psuedomonas aeruginosa, carbapenem-resistant Acinetobacter baumannii, colistin-resistant Enterobacteriaceae, vancomycin-resistant Enterococci, and methicillin-resistant S. aureus were less common. These findings suggest extensive contamination by antibiotic-resistant bacteria in hospital and community environment in Thailand.

Characteristics and formation mechanism of intestinal bacteria particles emitted from aerated wastewater treatment tanks

Aeration tanks in municipal wastewater treatment plants (WWTPs) are regarded as sources of bioaerosols, often containing particles and microbes. In this study, intestinal bacteria were investigated from biochemical reaction tanks (BRTs) of six municipal WWTPs. It was observed that 86 CFU/m3 of intestinal bacteria (in average) occurred in the BRTs installed surface aerator, which was higher than those adopted submerged aeration (67 CFU/m3 in average). 62.72% of fine particles were observed in the BRTs supplied oxygen by submerged aerator, while 75.73% of coarse particles emitted during surface aeration. Pseudomonas sp., Serratia sp. and Acinetobacter sp. were identified as pathogenic bacteria presented in the intestinal bacteria population and most of them existed initially in water or sludge, particularly in water surface. The emission level and particle size distribution were significantly correlated with aeration mode adopted by the WWTPs. The bioaerosols particles emitted from surface aeration process was higher than that from submerged aeration process. Meanwhile, the BRTs with submerged aerators released more fine particles, which can get into the alveoli and represented the potential challenge to human health. Canonical correspondence analysis results exhibited that population of intestinal bacteria had a positive correlation with aeration rate and water quality. As the intestinal bacteria in the bioaerosols emitted from the WWTPs may pose a potential risk to onsite operators, aeration tanks in WWTPs should be paid more attention as a source of intestinal bacterial emissions.

Leaf-cutter ants engineer large nitrous oxide hot spots in tropical forests.

Though tropical forest ecosystems are among the largest natural sources of the potent greenhouse gas nitrous oxide (N2O), the spatial distribution of emissions across landscapes is often poorly resolved. Leaf cutter ants (LCA; Atta and Acromyrmex, Myrmicinae) are dominant herbivores throughout Central and South America, and influence multiple aspects of forest structure and function. In particular, their foraging creates spatial heterogeneity by concentrating large quantities of organic matter (including nitrogen, N) from the surrounding canopy into their colonies, and ultimately into colony refuse dumps. Here, we demonstrate that refuse piles created by LCA species Atta colombica in tropical rainforests of Costa Rica provide ideal conditions for extremely high rates of N2O production (high microbial biomass, potential denitrification enzyme activity, N content and anoxia) and may represent an unappreciated source of heterogeneity in tropical forest N2O emissions. Average instantaneous refuse pile N2O fluxes surpassed background emissions by more than three orders of magnitude (in some cases exceeding 80 000 µg N2O-N m-2 h-1) and generating fluxes comparable to or greater than those produced by engineered systems such as wastewater treatment tanks. Refuse-concentrating Atta species are ubiquitous in tropical forests, pastures and production ecosystems, and increase density strongly in response to disturbance. As such, LCA colonies may represent an unrecognized greenhouse gas point source throughout the Neotropics.

Experimental and numerical investigation of flow patterns in shallow rectangular reservoirs with symmetrically positioned inlet and outlet channels

ABSTRACT Shallow flows correspond to turbulent flows whose horizontal dimensions are considerably larger than the vertical one. In Hydraulic Engineering, they refer, e.g., to stormwater basins, stabilization ponds for wastewater treatment and aquaculture tanks. Since they involve low flow velocities, a continuous settling process often affects such shallow reservoirs. Therefore, it is important to expand the knowledge about the influence of its geometry on the hydrodynamic behavior and the sedimentation tendency. This paper aims to analyze flow patterns in a rectangular reservoir with symmetrically positioned upstream and downstream channels, taking into account three different flow rates under steady flow regime (0.50, 1.25 and 3.40 L/s). Experimental tests were performed in a laboratory prototype, consisted of a 3.0 m long and 2.0 m wide reservoir, with a maximum depth of 0.30 m. Also, it was applied the WOLF 2D software for numerical modeling of all variants. Experimentally, a symmetrical hydrodynamic behavior was observed only for the lowest flow rate, while the flow pattern was asymmetrical for the other cases. On the other hand, the numerical model indicated hydrodynamic symmetry for all scenarios.

Production of Methane From Microalgae Biofilms Growing in Wastewater Treatment Plants in the Canary Islands

Two recurrent topics among the scientific community are the use of microalgae in wastewater treatment plants as a biological agent for nutrient removal, and, more recently, the use of microalgae for biofuel production. In this study we have analysed the possibility of coupling these two processes, using microalgae that naturally form biofilms on wastewater treatment tanks to produce methane. The proposal is to develop a low cost, environmental friendly methodology, with the economical and environmental advantages of enhancing the removal of nutrients from wastewater, and producing sustainable biofuel. A methane assay using microalgae biofilms from the primary and secondary treatment tanks from a wastewater treatment plant (WWTP) on the Canary Islands (EDAR-del Sureste, Gran Canaria, Spain) showed that, when this substrate is added to a suitable methanogenic bacteria, in this case marine sludge from a fish farm, it gives a methane yield of 0.104 Nm3 kg-1 VS. We also checked the in situ biomass yield of the biofilm (3.16 g AFDW m-2 d-1 and 7.71 g AFDW m-2 d-1, for the primary tank and secondary tank respectively), and the growth of this biofilms in photobioreactors (PBR). When grown in PBR, the algae composition of biofilm from the primary tank becomes dominate by a unicellular chlorophyta and produces 0.24 kg AFDW m- 3 d-1 of biomass; while biofilm from the secondary tank becomes dominated by the filamentous chlorophyta Stigeoclonium, and has a biomass yield of 0.48 kg AFDW m-3 d-1. The biofilms growing the WWTP of the EDAR del Sureste, in Gran Canaria, are a free naturally available source of biomass, and we have shown in this study that this biofilm, besides being used as a natural agent for nutrient removal in a WWTP, it has also the potentialof being used as a low cost, green source of biomass for methane production.

Portable and Disposable Paper-Based Fluorescent Sensor for In Situ Gaseous Hydrogen Sulfide Determination in Near Real-Time

Hydrogen sulfide is found in many environments including sewage systems, petroleum extraction platforms, kraft paper mills, and exhaled breath, but its determination at ppb levels remains a challenge within the analytical chemistry field. Off-line methods for analysis of gaseous reduced sulfur compounds can suffer from a variety of biases associated with high reactivity, sorptive losses, and atmospheric oxidative reactions. Here, we present a portable, online, and disposable gas sensor platform for the in situ determination of gaseous hydrogen sulfide, employing a 470 nm light emitting diode (LED) and a microfiber optic USB spectrometer. A sensing layer was created by impregnating 2.5 μL (0.285 nmol) of fluorescein mercury acetate (FMA) onto the surface of a micropaper analytical device with dimensions of 5 × 5 mm, which was then positioned in the optical detection system. The quantitative determination of H2S was based on the quenching of fluorescence intensity after direct selective reaction between the gas and FMA. This approach enabled linear calibration within the range 17-67 ppb of H2S, with a limit of detection of 3 ppb. The response time of the sensor was within 60 s, and the repeatability was 6.5% (RSD). The sensor was employed to monitor H2S released from a mini-scale wastewater treatment tank in a research laboratory. The appropriate integration of optoelectronic and mechanical devices, including LED, photodiode, pumps, and electronic boards, can be used to produce simple, fully automated portable sensors for the in situ determination of H2S in a variety of environments.

Gas Extraction from Sludge as Acquired from Oxidation Ponds of Community Wastewater and Cassava-Factory Wastewater Treatment through Nature-by-Nature Processes

The study was aimed on determining the gas volume from sludge of oxidation ponds for community wastewater treatment and UASB tank of cassava factory for wastewater treatment in which the organic matters of both units were digested through the nature-by-nature process. The amounts of oven- dry weight sludge about 200 g were collected in the light brow glass bottle with 2.5-l capacity. The fermentation of organic matters in sludge is the process to produce gases and being transferred to store in chamber by fluid displacement. The gases from sludge of oxidation pond was occurred on the second day and the maximum on the sixth day with the rate of 70 ml/d and average of 36.02 ml/d (total 360.23 ml for 10 days) while cassava factory sludge found the maximum volume on the first day with the rate of 142.6 ml/d and average of 72.2 ml/d (total 649.97 ml for 9 days). In other words, the oxidation pond sludge can produce gas 1.8 ml/g (oven dry weight) while the cassava factory sludge found gas 3.25 ml/g (oven dry weight). Research results found gases of oxidation pond sludge on the range of methane concentration between 545,686 – 9,560,606 ppm, hydrogen sulfide 55.94 to 360.27 ppm, and ammonia ND to 36.22 ppm, while the cassava factory sludge found methane gas concentration between 729,404 to 9,900,837 ppm, hydrogen sulfide 5,894 to 68,050 ppm, and ammonia ND to 44.15 ppm.

Batch Kinetics and Effects of Process Parameters for Biodegradation of Reactive Black 5 in an Aerobic Mixed Microbial Culture

Mixed microbial culture used in this study was developed from sludge that was taken from local textile wastewater treatment tank. Acclimatization process was performed before starting the biodegradation experiment to obtain a microbial culture with high degradation properties. Kinetic studies by the mixed microbial culture were determined quantitatively for the model pollutant, Reactive Black 5 (RB 5). By using Michaelis-Menten model, the constants were found to be 11.15 mg L-1 h-1 and 29.18 mg L-1 for V m and Km respectively. The values of kinetic constants for Monod model were found to be 33.11 mg L-1 cell h-1 for the maximum specific microbial growth rate, µm and 86.62 mg L-1 for Monod constant, K5. The effects of process parameters such as pH, inoculum size and initial dye concentration on the biodegradation of azo dye, RB 5 were systematically investigated. Maximum removal efficiencies observed in this study were 75% for pH 6, I 00% for 15% inoculum concentration and 75% for 20 ppm of initial dye concentration.

Batch Kinetics and Effects of Process Parameters for Biodegradation of Reactive Black 5 in an Aerobic Mixed Microbial Culture

Mixed microbial culture used in this study was developed from sludge that was taken from local textile wastewater treatment tank. Acclimatization process was performed before starting the biodegradation experiment to obtain a microbial culture with high degradation properties. Kinetic studies by the mixed microbial culture were determined quantitatively for the model pollutant, Reactive Black 5 (RB 5). By using Michaelis-Menten model, the constants were found to be 11.15 mg l-1 h-1 and 29.18 mg l-1 for Vm and Km respectively. The values of kinetic constants for Monod model were found to be 33.11 mg l-1 cell h-1 for the maximum specific microbial growth rate, µm and 86.62 mg l-1 for Monod constant, Ks. The effects of process parameters such as pH, inoculum size and initial dye concentration on the biodegradation of azo dye, RB 5 were systematically investigated. Maximum removal efficiencies observed in this study were 75% for pH 6, 100% for 15% inoculum concentration and 75% for 20 ppm of initial dye concentration.

Investigation of residence time distribution and local mean age of fluid to determine dead-zones in flow field

Residence time and local mean age of flare important parameters of the fl uid fl ow, with which we are able to detect the functioning and non-functioning zones. It is a novel approach to estimate the effect of dead-zones on chemical and biological processes. In this paper, we introduce a numerical tracer study, which is calibrated by fi measurements and which is applied in different cases such as settling tank and aeration tank of wastewater treatment. Using an advective-diffusive passive scalar transport equation, the age of the fl uid can be calculated. It also shows the short-circuits and dead-zones of the fl uid and this corresponds with our observations. This method helps eliminate potential hydraulic problems at the early stage of design. Settling tanks in the wastewater treatment have a key role in the separation of suspended solids and sludge fl ocks. The design of these tanks is based on the ATV-A131 standard (1), which takes into account only the global parameters of the fl ow, e.g. average residence time, but in many cases the inequalities inside the tank may have serious effect on effl uent quality. In this paper, we are fi rst and foremost interested in the detection of dead-zones, where the mixing is adverse due to low velocity, high residence time and fl uid age. In aeration tanks, for example, anaerobic zones may develop because microorganisms consume the oxygen. There is mass transfer between the fl ow and dead-zone because of the presence of turbulence; how- ever, this is much less than the effect of convective transport. On the other hand, hydraulically inactive zones are redundant and these increase the cost of operation. Computational fl uid dynamics is widely applied in wastewater treatment tank design (2-4)) because with the knowledge of hydraulic phenomena, the understanding of biochemical processes could be improved. One signifi cant linking parameter between the hydraulics and biology is residence time; therefore, it is essential to know the precise value for every point. Residence time dis- tribution (RTD) can be measured experimentally (5). In pulse experiment, the tracer is mixed in a small volume of fl which is introduced to the reactor in a very short time interval (Dirac-delta function) and the response function is measured at the outlet. The tracer should be a conservative material without any background concentration of the wastewater. The response function shows the changes in tracer concentration in the course of time, from which we can estimate the hydraulic behavior of the tank. RTD calculations can be performed numerically, and they can be compared to the results of the fi eld measurement. This paper deals with circular fl ow reactors, one aeration tank and one radial fl ow settling reactor. The fi rst is designed as a fully mixed reactor, but the RTD investigation demonstrated that there is a short-circuit, where the nutrients could fl ow through the reactor rapidly and did not have enough time for biodegradation. Circular radial fl ow settling tanks generally have problems with short-circuiting and the wind also could have an infl uence on the fl ow regimes.

The role of anaerobic sludge recycle in improving anaerobic digester performance

Solids retention time (SRT) is a critical parameter for the performance of anaerobic digesters (AD) in wastewater treatment plants. AD SRT should increase when active biomass is input to the AD by recycling anaerobic sludge via the wastewater-treatment tanks, creating a hybrid aerobic/anaerobic system. When 85% of the flow through the AD was recycled in pilot-scale hybrid systems, the AD SRT increased by as much as 9-fold, compared to a parallel system without anaerobic-sludge recycle. Longer AD SRTs resulted in increased hydrolysis and methanogenesis in the AD: net solids yield decreased by 39–96% for overall and 23–94% in the AD alone, and AD methane yield increased 1.5- to 5.5-fold. Microbial community assays demonstrated higher, more consistent Archaea concentrations in all tanks in the wastewater-treatment system with anaerobic-sludge recycle. Thus, multiple lines of evidence support that AD-sludge recycle increased AD SRT, solids hydrolysis, and methane generation.

Isolation and characterization of Planctomycetes from the sediments of a fish farm wastewater treatment tank

The increasing ecological significance of Planctomycetes and the still limited knowledge of this group prompted us to obtain cultured isolates from the sediment of a treatment water recycling tank of a marine fish farm. Presence of strains from this group was assessed in the sediments and water column of the tank. Eleven isolates were obtained from the sediment sample by exploiting Planctomycetes natural resistance to several antibiotics and their capacity to degrade organic matter. Based on morphological characteristics and resistance to antibiotics, Planctomycetes were identified. Their phylogenetic affiliation was confirmed by the sequence analysis of the 16S rRNA gene that revealed the presence of a group of 6 isolates closely related to Rhodopirellula baltica and a cluster of 5 isolates with 97.7-97.9 % of similarity to this species, which probably are a different species of Rhodopirellula. ERIC-PCR profiles showed a higher discrimination within the two groups and allowed the identification of nine different genotypes within the isolated strains. This work corroborates the association of Rhodopirellula spp. with fish farm environments.