Waste Stabilization Pond System Research Articles

Effect of sunlight on three stratifications of waste water from a waste stabilization pond

Experimental studies on stratification were conducted on a waste stabilization pond system at the University of Nigeria, Nsukka, Nigeria. This was done to ascertain the effect of stratification due to sunlight on pond parameters. An experimental approach was adopted which involved pouring wastewater into a glass column apparatus and exposing to sunlight for 7, 14, and 21 days. The statues of 16 physicochemical and microbiological parameters were investigated in the three strata under consideration. Analysis of the samples collected at depths A, B and C, 30cm apart, starting from the top indicated different values of temperature, pH, and nutrients. Maximum values of temperature (32.9 0C), pH (7.9), turbidity (3.46 NTU), and iron (1.86 mg/l), were recorded at the top layer; while the concentration of conductivity (906 μS/cm), total dissolved solids (589 mg/l), BOD5 (400mg/l), ammonia (290 mg/l), total coliform (126,000 cfu/100ml), and E. Coli (99,000 cfu/100ml) were highest at bottom layer. Conductivity, total dissolved solids, turbidity, iron, phosphorus and nitrates fell within World Health Organization (WHO) guidelines. A combination of sunlight with high pH and oxygen concentrations is needed for sunlight to have very significant effects. It is recommended that WSPs be designed with the consideration given to pond dimensions that will provide a wider surface area for sufficient sunlight and oxygen to be acquired.

Decentralized sanitation solutions for temporal Internally Displaced people (IDPs) and refugees camps and residential complexes in Duhok province – Case study

The conditions of the settlements are often very poor with deficiencies in basic supplies like water. This study aims to: (i) assess the sanitation service level for Internally Displaced People (IDPs) and refugee camps in Duhok province / Kurdistan of Iraq (ii) assess the performance of wastewater treatment plants (WWTPs) and offer different scenarios to improve the sanitation service level in the Duhok province (iii) propose various decentralized treatment approaches. To demonstrate the efficiency of WWTPs, samples of generated wastewater at the effluent of 12 residential projects were collected to conduct the COD test. The results of COD test were found to exceed the permissible level of 100 mg/L set by Iraqi wastewater standard except in New Zakho and Avro city projects. The highest generation rates of grey and black wastewater were in Chamishko and Kaberto1 IDP camps and were 1013 and 3000 m 3 /day respectively. Both Avro city and War city residential complexes were notably discharging the highest rates of wastewater at the effluent with 5610 and 2484 m 3 /day respectively. Lelav city, New Jin city, and Dabin projects were found to have the maximum organic loading rate of COD with 745, 578, and 332 kg/day respectively. This study proposed Waste Stabilization Pond (WSP) systems to be constructed in both Domiz1 refugee camp and Chameshko IDP camp. In order to be more achievable, it is suggested that the regulations of disposed wastewater at the effluent be amended and categorized on a class basis rather than using a single effluent number.

Characterization and evaluation of waste stabilization pond systems in Namibia

Abstract Waste stabilization ponds (WSP) exist worldwide to treat wastewater, especially in warm climates. They are characterized by simple operation and maintenance and over 50 years many WSP were built in urban communities in Namibia. This study characterized and evaluated nine of these WSP systems in terms of their influent and effluent water quality and compared them with the requirements for water reuse in agriculture. In their current state none of them adhered with the Namibian or the new European reuse standards, especially due to tCOD concentrations above 100 mg/L caused by high algal fractions in the pCOD. The algae related chlorophyll-a concentrations correlated linearly with the pCOD and this correlation can therefore be used to fractionate the tCOD for further judgement. Additionally, microbial community analyses determined the composition of pathogens in the WSP influent and effluent, this helped to assess potential risks and distinguish between potentially toxic and non-toxic cyanobacteria. The EU requirement of less than 1,000 E. coli per 100 mL for fodder crop irrigation was only achieved with one WSP system which was enhanced with additional pre- and post-treatment. This research delivers a first overview of the current situation and can be used as basis to establish possible enhancement measures for existing WSP as well as to investigate possible effluent application in agricultural irrigation.

Laboratory-scale waste stabilisation pond development

The present study describes the development of a laboratory-scale waste stabilisation pond (WSP) system, undertaken in order to investigate the effects of hydraulic, physicochemical, microbial and physical parameters on wastewater treatment. Previous studies have focused predominantly on hydraulic characteristics. This system was engineered at a scale much smaller than had previously been seen in the literature. The scale of the model used here allows for improved optimisation at a shorter time scale that would be seen for larger pilot-scale systems. Additionally, with the addition of viruses, a smaller scale model allows for more control over viral concentration used. Once constructed, the system was dosed with wastewater from a wastewater treatment plant and both the influent and effluent were monitored using common testing methods as well as direct viral analysis. Successful wastewater treatment was seen in terms of reduction of indicator bacteria and virus, as determined by culture-based methods. This treatment and the associated stabilisation of physicochemical parameters such as dissolved oxygen and pH, indicates the successful development of a microbial community within the laboratory-scale WSP.

Pilot-Scale Investigation of Floating Treatment Wetlands as Retrofits to Waste-Stabilization Ponds for Efficient Domestic Wastewater Treatment

This study investigates the efficacy of floating treatment wetlands (FTWs) for retrofitting waste-stabilization ponds (WSPs) operating in cold continental climates, such that in Alberta, Canada. The objective was to determine whether WSPs augmented with FTWs could achieve equal or superior treatment efficiency at shorter hydraulic retention times (HRTs of 25–45 days) than those required in the conventional WSPs (60–365 days). A field study was carried out on treatment of domestic wastewater in a two-stage pilot-scale FTW mesocosm (i.e., FTW treatment train composed of Stage 1 and Stage 2 FTW cells (S1-FTW→S2-FTW), with an overall volume of 84 m3 and 41.85 m3 per cell). An identical system without FTW served as a control (i.e., control treatment train of S1-C→S2-C). Overall, the FTW-augmented WSP system achieved greater treatment of 5-day biochemical oxygen demand (BOD5), total suspended solids (TSS), total nitrogen (TN), ammonium nitrogen (NH4+-N), dissolved reactive phosphorus (DRP), and total phosphorus (TP) than the control. The corresponding removal efficiencies were 91.5% versus 85.0%, 91.3% versus 87.7%, 85.0% versus 75.6%, 93.9% versus 86.1%, 77.6% versus 57.7%, and 75.8% versus 58.7%, with a statistically significant difference (p<0.05) for all except TSS. This difference in performance resulted from the better performance of the Stage 1 FTW cell for BOD5, TN, and NH4+-N removal, and the Stage 2 FTW cell for DRP and TP removal. Simultaneous nitrification-denitrification (SND) occurred in the FTW treatment train, whereas only nitrification occurred in the control treatment train, which resulted in statistically higher TN removal efficiency in the former. Contribution of plant uptake to phosphorus removal was marginal (6.76%) and adsorption-desorption on solid particles was assumed to be the major removal pathway. The FTWs generally decreased the physicochemical parameters, with stronger effects on diurnal variations than seasonal fluctuations. The effect of FTW on daily physicochemical conditions played a key role in superior performance of FTW treatment.

Monitoring Microbial Populations and Antibiotic Resistance Gene Enrichment Associated with Arctic Waste Stabilization Ponds.

Wastewater management in the Canadian Arctic is challenging due to climate extremes, small population sizes, and lack of conventional infrastructure for wastewater treatment. Although many northern communities use waste stabilization ponds (WSPs) as their primary form of wastewater treatment, few studies have explored WSP microbial communities and assessed effluent impacts on receiving waters from a microbiological perspective. Here, we used 16S rRNA gene and metagenome sequencing to characterize WSP and receiving water microbial communities for two time points bracketing the spring WSP thaw in Baker Lake (Nunavut) and compared these results to other Nunavut WSPs in Cambridge Bay and Kugluktuk. Most amplicon sequence variants (ASVs) recovered from these WSP samples belonged to the phylum Proteobacteria, with considerable variation between the three locations and only six ASVs shared among the WSPs at >0.2% relative abundance. Wastewater indicator ASVs for the Baker Lake WSP were identified, and few indicator ASVs were detected in samples originating from other upstream or downstream sites. The metagenomic data revealed a strong enrichment of antibiotic resistance genes for WSP samples relative to downstream and reference samples, especially for genes associated with macrolide resistance. Together, our results provide a baseline characterization for WSP microbial communities, demonstrate how indicator ASVs can be used to monitor attenuation and dilution of effluent microorganisms, and reveal that WSPs can serve as hot spots for antibiotic resistance genes.IMPORTANCE Given that the microbial communities of Arctic waste stabilization ponds (WSPs) are poorly studied to date, our characterization of multiple WSP systems and time points provides important baseline data that will assist with ongoing monitoring of effluent impacts on downstream aquatic ecosystems in the Arctic. This research also identifies indicator amplicon sequence variants (ASVs) of WSPs that will be helpful for future monitoring for WSP effluent attenuation and demonstrates that WSP microbial communities are enriched in antibiotic resistance genes. Given operational and infrastructure changes anticipated for wastewater treatment systems in the Arctic, baseline data such as these are essential for further development of safe and effective wastewater treatment systems.

Evaluation of contaminants removal by waste stabilization ponds: A case study of Siloam WSPs in Vhembe District, South Africa

Waste stabilization ponds (WSPs) are widely used for wastewater management owing to the simplicity of their design, low cost and the use of low-skilled operators. This study was carried out to assess the efficiency of a WSP system in reducing the levels of contaminants in hospital wastewater in a rural area of South Africa and to evaluate the current management of the WSP system. Sampling was conducted monthly from January to June 2014. Physicochemical and microbiological parameters were monitored using standard methods. The microbiological parameters (Escherichia coli and enterococci) in the effluent were higher than those in the influent in some sampling months. Also, low pathogen removal efficiency (<1 log reduction) was recorded. The chemical oxygen demand (COD) in the effluent (82–200 mg/L) exceeded the South African Department of Water Affairs for wastewater discharge guideline value of 75 mg/L although reduction efficiencies of 7.7%, 49.1% and 31.1% were observed for the months of February, April and June, respectively. The WSP system did not show a general trend of contaminant reduction except for Zn (5.5–94.8%). The Siloam WSP is not functioning properly and is releasing effluent of poor quality into the receiving river. It is recommended that the WSP system be expanded to cater for the extra load of wastewater it receives, also desludging should be performed as recommended for such systems. Continuous monitoring of the system for compliance to regulatory guideline should be routinely performed.

Performance evaluation and coefficients of reliability for waste stabilization ponds in northeast Brazil

This paper assesses the reliability of Waste Stabilization Ponds (WSP) and proposes an alternative approach to WSP design based on the calculation of coefficient of reliability (COR) from an acceptable measure of violation of discharge standards. For that, data were collected from 10 full-scale systems operating in Northeast Brazil. All systems receive predominantly domestic effluent and are composed of one facultative pond and two serial maturation ponds. Different levels of restriction for effluent discharge were considered regarding the parameters: BOD, COD, total suspended solids, ammonia and thermotolerant coliforms. The Log-normal Probability Distribution Function (PDF) was able to represent the behavior of the concentration data in the effluent and, therefore, allowed the COR calculation. The COR was obtained from the coefficient of variation (CV) of the concentrations and the standardized normal variable associated with a 95% probability of non-exceedance. The observed dispersion of the results proved to be detrimental to the adoption of a single COR value for the evaluated parameters. In addition, the comparison between observed and design/operational concentration for optimal performance showed that the 95% reliability scenario represents a less achievable target for WSP systems.

Chemical removal in waste stabilisation pond systems of varying configuration

Better chemical removal in waste stabilisation ponds was linked to the presence of a maturation pond, higher solar irradiation, and warmer temperatures.

Effect of initial cod concentration and the fraction of N/P on treatment ability of Para grass (Brachiaria mutica) vegetation in the stabilization pond

Stabilization pond which is covered by aquatic plant is a environmentally friendly method to treat wastewater. In this study, stabilization pond using Para grass vegetation is applied to treat industrial wastewater and study the effect of intitial COD concentration and the N/P ratio on treatment abliity of para grass vegetation in the stabilization. The influent flow rate is controlled at 0.18 m3/h (corresponding to a retention time of 5.3 days). As inflow COD concentration is 203 ± 5.9 mg/L, COD treatment efficiency reaches 59.6 – 61.7%. When COD concentration in the input wastewater is 349.2 ± 4.5 mg/L, COD removal efficiency decreased to 55.7 0.9%. Continue to increase input COD concentration in the input to 512,6 ± 14,7 mg/l, COD treatment efficiency reduce to 47.9±0.6%. However, when increasing the input COD concentration corresponding to increasing the organic loading rate into the model, reached 10.270 kgCOD/ha.day at COD concentration = 512.6 ± 14,7 mg/L, twice higher than the organic loading rate of the model since COD concentration = 203 ± 5.9 mg/L. The result shows strong adaptability and wastewater treatment ability of facultative waste stabilization pond system covered by Para grass, although the input COD concentration or organic load increase more than doubled. The study also showed that the treatment efficiency of total nitrogen (TN) tends to increase when COD concentration in influent increases, with treatment effiency has reached from 57.2 to 76.4%. Besides, the fraction of nitrogen and phosphorus in influent also surveyed in this study. The fraction of N/P selected to survey in the study is approximately 2.26, 4.16 and 6.11. The results show that when increasing the N/P ratio, the efficiency of Total Nitrogen treatment tends to increase. At N/P ratio = 2.26 ± 0.19, even though the concentration of TN in the inlet is low, but nitrogen metabolism still takes place in the experimental model, so outlet TN concentration decrease to very low. The COD treatment efficiency increases gradually when increasing the N/P ratio. The output COD match Vietnam discharge standard QCVN 40:2011/BTNMT. These results show potential for applying the stabilization pond which is covered by Para grass for treating concentrated industrial wastewater.

First-Order Removal Rates for Organic Matter in Full-Scale Waste Stabilization Pond Systems in Northeastern Brazil

This paper investigated the organic matter removal in waste stabilization ponds (WSP) based on ten full-scale wastewater treatment plants (WWTP) located in Rio Grande do Norte, Northeast Brazil. Although many systems are operating at high organic loading rates, in some cases, over 1000 kg BOD5 ha−1 d−1, the ponds promoted satisfactory removals of biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). The first-order removal rates (k) for BOD5 and COD were obtained by assuming the ideal hydraulic patterns of completely mixed and plug-flow models. The k values proved to be a function of physical and operational parameters that affect fluid movement in a pond. The increase in the organic loading rate caused an increase in first-order removal rates. Moreover, increasing the ratio between hydraulic retention time (HRT) and depth (H) led to a reduction in k values. This information can be adapted into predictive models to be applied in WSP designs with similar characteristics. In comparison with the empirical equations reported in the literature, these models lead to removal rates more appropriate to the local reality.

Monte Carlo simulation in the evaluation of failure probability in waste stabilization ponds

This study used Monte Carlo simulation as a methodology to analyze the percentage of failure in Waste Stabilization Pond (WSP) systems in meeting the discharge standards in water bodies. We used monitoring data from 10 full-scale WSP in operation in Rio Grande do Norte, northeast Brazil. The Kolmogorov - Smirnov (KS) adherence test followed by the Akaike Information Criterion (AIC) allowed the selection of the most representative Probability Distribution Function (PDF) of each sample set. Simulations with 3000 iterations allowed us to construct synthetically the selected distributions and, thus, to calculate the percentages of non-compliance with the standard of interest. Among the simulated parameters, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of unfiltered samples showed the highest percentage of failure over the pond series. The failure percentages of thermotolerant coliforms and pH parameters were correlated with physical and operational variables such as hydraulic retention time, depth and organic loading. The information presented provides an overview of the occurrence of failure and the inherent risks of stabilization pond treatment technology.

Integration of water hyacinth plants into waste stabilization ponds: a case study of Donnybrook 4 Sewage Ponds in Mabvuku-Tafara, Harare, Zimbabwe

Donnybrook Waste Stabilization Ponds (WSP) are overloaded and water hyacinth plants have infested the ponds. The study assessed the feasibility of integrating the problematic water hyacinth plants into the current treatment process. Grab samples of influent and effluent for each pond were collected between 28 March and 23 April 2019 and the analysis was done following standard APHA methods. Parameters considered include pH, turbidity, TDS, TSS, TN, TP, BOD, and COD. The raw sewage mean pH, turbidity, TDS, TSS, TN, TP, BOD, and COD were 8.08, 580 NTU, 1639mg/L, 1294mg/L, 78mg/L, 8.16mg/L, 287mg/L, and 887mg/L. The mean pH, turbidity, TDS, TSS, TN, TP, BOD, and COD in the effluent from the existing maturation pond, control pilot pond, and water hyacinth pilot pond were 7.7, 7.7, and 7.3; 75, 67, and 47 NTU; 861, 758, and 668mg/L; 276, 172, and 82mg/L; 27, 28, and 17mg/L; 4, 5.28, and 4mg/L; 114, 52, and 30mg/L; and 243, 122, and 81mg/L. It was concluded that the water hyacinth may be integrated into the WSP system to enhance contaminant removal. The water hyacinth in the ponds should be harvested periodically to avoid secondary organic and nutrient loading from dead plants.

Diurnal variation of the water quality parameters in the waste stabilization ponds (WSPs) for water treatment of integrated multi-trophic aquaculture (IMTA) ponds with closed re-circulation system

Organic wastes from Floating Fish Cage Aquaculture (FCA) activities have polluted many inland water bodies, from small reservoirs to major lakes in Indonesia. It has become a national priority to restore ecosystem health in Lake Maninjau. The lake has suffered from the harmful effects of approximately 17,000 units of FCA on its surface area. Better FCA practices that would improve its adjacent water quality have been proposed. The FCA should utilize a more excellent net that would confine its waste. Using a connection pump, the wastewater within this net could then be circulated into a wetland system for its water quality improvement. The proposed wetland system consists of a series of Waste Stabilization Ponds (WSP) and Constructed Wetland Compartments. For the initial stage, a study has been conducted to test the performance of the WSP with approximately six days of hydraulic retention time (HRT) to improve water quality from the Integrated Multi-Trophic Aquaculture (IMTA) ponds in the Prototype Laboratory of Research Centre for Limnology-LIPI. Two major problems in IMTA, namely organic deposition and low of dissolved oxygen (DO), especially concerning its diurnal variations in the system, have not been studied yet. Water qualities of the WSP ponds were measured every 2 hours for three days (22-25 May 2019). Water quality parameters measured were pH, conductivity, dissolved oxygen (DO), turbidity, temperature, oxidation and reduction potential (ORP), and total dissolved solids (TDS). A closed re-circulation within the WSP system was then applied for the last two days of the study period. The result showed that DO values in the effluent pond during the day were significantly higher than the night. In the maturation and facultative ponds, DO values difference ranged from 2.5-3 mg/L and 1.1-4.4 mg/L, respectively. The highest DO (5.98 mg/L) was measured in the maturation pond at 3.00 PM and values were lowest almost to 0 mg/L during the first day in the anaerobic ponds. While for turbidity, the highest was observed in the anaerobic ponds for 41 NTU and were decreased to stable values of an average of 5.3 NTU in the maturation pond on the third day. At the end of the observation, marked increase of DO and decrease in turbidity have occurred in the system. A closed recirculation system within WSP can be used as an option to increase the performance of the wetland system.

Acinetobacter baumannii detected on modified charcoal-cefoperazone-deoxycholate agar in a waste stabilization pond.

Campylobacter is a recommended reference pathogen for the verification and validation of water recycling schemes in Australia and globally. In a larger study investigating the efficacy of pathogen removal in waste stabilization ponds (WSP), we cultivated bacteria from wastewater samples on modified charcoal-cefoperazone-deoxycholate agar (mCCDA) targeting the growth of Campylobacter. A high number of colonies characteristic of Campylobacter grew on this selective medium, but this did not correlate with qPCR data. Using primers targeting the 16S rRNA gene, and additional confirmatory tests to detect VS1, ompA, blaOXA-51-like, blaOXA-23-like genes, we tested 80 random colonies from 10 WSP samples. All 80 were identified as Acinetobacter baumannii. Wastewater grab samples taken three times over 6 months throughout the WSP system showed removal of A. baumannii in the WSP at rates similar to that of Escherichia coli. Our study suggests that mCCDA agar is not a suitable medium for isolating Campylobacter from environmental samples and that A. baumannii can be used as an indicator for removal of pathogens in WSPs.

Evaluation of Occurrence, Concentration, and Removal of Pathogenic Parasites and Fecal Coliforms in Three Waste Stabilization Pond Systems in Tanzania.

In Tanzania, waste stabilization ponds (WSPs) are employed to treat wastewater, and effluents are used for urban agricultural activities. The use of untreated or partially treated wastewater poses risks of disease transmission, including parasitic and bacterial infections, to exposed communities. Little is known about the occurrence, concentration, and removal of parasites and fecal coliform (FC) bacteria in WSPs in Tanzania. This study evaluates the occurrence and concentration of parasites and FCs in wastewater, the efficiency of WSPs in removing parasites and FCs, and the validity of using FCs as an indicator of parasites. This was a cross-sectional study conducted between February and August 2018. Wastewater samples were collected from three WSPs located in the Morogoro, Mwanza, and Iringa regions. APHA methods were used to test physicochemical parameters. The modified Bailenger method and Ziehl–Neelsen stain were used to analyse parasites. Membrane filtration method was used to analyse FCs. Data were analysed using IBM SPSS version 20. Helminth egg removal ranged from 80.8% to 100%. Protozoan (oo)cyst removal ranged from 98.8% to 99.9%. The Mwanza WSP showed the highest FC reduction (3.8 log units (100 mL)−1). Both the parasites and FCs detected in the effluents of assessed WSPs were of higher concentrations than World Health Organization and Tanzania Bureau of Standards limits, except for helminths in the Morogoro WSP and FCs in the Mwanza WSP. FCs were significantly correlated with protozoa (p < 0.01) and predicted protozoa occurrence well (p=0.011). There were correlations between physicochemical parameters, parasites, and FC bacteria in the WSP systems. Inadequate performance of these systems may be due to lack of regular maintenance and/or systems operating beyond their capacity. FC indicators were observed to be a good alternative for protozoa monitoring, but not for helminths. Therefore, during wastewater quality monitoring, helminths should be surveyed independently.

Integrated simple ceramic filter and waste stabilization pond for domestic wastewater treatment

Abstract A laboratory scale study was undertaken to investigate the applicability of a simple ceramic filter (SCF) when integrated into a Waste Stabilization Pond (WSP) system and was operated under different experimental conditions. The SCF was made of locally available materials: 80% soil and 20% rice bran on weight basis. Scanning electron microscope with energy-dispersive X-ray spectrometry (SEM/EDS) analysis indicated mainly the presence of C, O, Si, Fe and Al. The SCF was submerged in rectangular pond reactors made of glass sheets. Synthetic wastewater was fed continuously into the reactors that contained algae (mainly Scenedesmus) mixed liquor; effluent through the integrated filter was collected using a suction pump. Filtration efficiency, organic removal performance, flux and HRT effects, organic loading rate optimization and SCF maintenance were investigated through different experimental conditions. High organic removal was achieved due to efficient filtration performance. Nitrogen removal was critically dependent on organic carbon availability. A linear relationship between flux, HRT, BOD loads and clogging frequency was obtained. Reversible fouling of SCF was observed during the experiment and simple physical cleaning was found effective for its maintenance. In general, the results of this study indicated that the low cost SCF can be integrated with WSP for treating domestic wastewater, after identifying optimum hydraulic loadings and associated size and shape.

Decay rates of Escherichia coli, Enterococcus spp., F-specific bacteriophage MS2, somatic coliphage and human adenovirus in facultative pond sludge

The purpose of this study was to evaluate the efficacy of a waste stabilization pond (WSP) system to reduce pathogen contaminants in sludge. This included examining the factors that influence the fate and concentration of human pathogens and their indicators in two sludge layers. The decay rates of five study microorganisms were determined under in-situ conditions at a WSP. The background levels of fecal origin microorganisms were consistently detected (ranging: Escherichia coli 104 to 106, enterococci 101 to 103, F-specific bacteriophage (MS2) 101 to 103 and somatic coliphage 101 to 104 colony-forming units (CFU) mL−1, as well as 101 to 102 human adenovirus gene copies mL−1) in the primary facultative pond. Among microorganisms tested, the bacteria generally decayed faster than adenovirus and bacteriophage, particularly in the upper sludge layer. Due to the observed regrowth of E. coli, it may have a limited value as an indicator for pathogen removal in the wastewater stabilization ponds. The abundance of E. coli numbers within the pond biome followed changes in pond temperature over time. The results of the study suggest that viruses could survive for a long time, particularly in deeper layers (>1 metre) in the sludge, during winter months (T90 = 156 d). The presence of human pathogens in WSP sludge, in particular viruses, may be a barrier to its beneficial reuse in agriculture. The results indicate that additional treatment of sludge may be required to mitigate potential public health risks from reuse of sludge for agricultural purposes.

Model-Based Analysis of Increased Loads on the Performance of Activated Sludge and Waste Stabilization Ponds

In a way to counter criticism on low cost-effective conventional activated sludge (AS) technology, waste stabilization ponds (WSPs) offer a valid alternative for wastewater treatment due to their simple and inexpensive operation. To evaluate this alternative with respect to its robustness and resilience capacity, we perform in silico experiments of different peak-load scenarios in two mathematical models representing the two systems. A systematic process of quality assurance for these virtual experiments is implemented, including sensitivity and identifiability analysis, with non-linear error propagation. Moreover, model calibration of a 210-day real experiment with 31 days of increased load was added to the evaluation. Generally speaking, increased-load scenarios run in silico showed that WSP systems are more resilient towards intermediate disturbances, hence, are suitable to treat not only municipal wastewater, but also industrial wastewater, such as poultry wastewater, and paperboard wastewater. However, when disturbances are extreme (over 7000 mg COD·L−1), the common design of the natural system fails to perform better than AS. Besides, the application of sensitivity analysis reveals the most influential parameters on the performance of the two systems. In the AS system, parameters related to autotrophic bacteria have the highest influence on the dynamics of particulate organic matter, while nitrogen removal is largely driven by nitrification and denitrification. Conversely, with an insignificant contribution of heterotrophs, the nutrient removal in the pond system is mostly done by algal assimilation. Furthermore, this systematic model-based analysis proved to be a suitable means for investigating the maximum load of wastewater treatment systems, and from that avoiding environmental problems and high economic costs for cleaning surface waters after severe overload events.

Further contributions to the understanding of nitrogen removal in waste stabilization ponds.

A set of experiments were conducted in Brazil in a pilot-scale waste stabilization pond (WSP) system (a four-maturation-pond series) treating an upflow anaerobic sludge blanket (UASB) reactor effluent. Over a year and a half the pond series was monitored under two flow rate conditions, hence also different hydraulic retention times and surface loading rates. On-site and laboratory trials were carried out to assess: (i) ammonia losses by volatilization using acrylic capture chambers placed at the surface of the ponds; (ii) organic nitrogen sedimentation rates using metal buckets placed at the bottom of the ponds for collecting settled particulate matter; (iii) nitrogen removal by algal uptake based on the nitrogen content of the suspended particulate matter in samples from the ponds' water column. In addition, nitrification and denitrification rates were measured in laboratory-based experiments using pond water and sediment samples. The pond system achieved high nitrogen removal (69% total nitrogen and 92% ammonia removal). The average total nitrogen removal rates varied from 10,098 to 3,849 g N/ha·d in the first and the last ponds, respectively, with the following fractions associated with the various removal pathways: (i) 23.5-45.6% sedimentation of organic nitrogen; (ii) 13.1-27.8% algal uptake; (iii) 1.2-3.1% ammonia volatilization; and (iv) 0.15-0.34% nitrification-denitrification.