M. von Sperling

Comparative performance evaluation of full-scale anaerobic and aerobic wastewater treatment processes in Brazil

This article evaluates and compares the actual behavior of 166 full-scale anaerobic and aerobic wastewater treatment plants in operation in Brazil, providing information on the performance of the processes in terms of the quality of the generated effluent and the removal efficiency achieved. The observed results of effluent concentrations and removal efficiencies of the constituents BOD, COD, TSS (total suspended solids), TN (total nitrogen), TP (total phosphorus) and FC (faecal or thermotolerant coliforms) have been compared with the typical expected performance reported in the literature. The treatment technologies selected for study were: (a) predominantly anaerobic: (i) septic tank + anaerobic filter (ST + AF), (ii) UASB reactor without post-treatment (UASB) and (iii) UASB reactor followed by several post-treatment processes (UASB + POST); (b) predominantly aerobic: (iv) facultative pond (FP), (v) anaerobic pond followed by facultative pond (AP + FP) and (vi) activated sludge (AS). The results, confirmed by statistical tests, showed that, in general, the best performance was achieved by AS, but closely followed by UASB reactor, when operating with any kind of post-treatment. The effluent quality of the anaerobic processes ST + AF and UASB reactor without post-treatment was very similar to the one presented by facultative pond, a simpler aerobic process, regarding organic matter.

Estimation of domestic wastewater characteristics in a developing country based on socio-economic variables

The paper presents the analysis of data related to the domestic wastewater characteristics from several areas situated in a large Brazilian city. Simple regression models are presented for the prediction of basic wastewater characteristics, such as water consumption (1/inhab.day), wastewater production (1/inhab.day), BOD load (g/inhab.dayj and BOD concentration (mg/l). The models are based on simple socio-economic variables, with special attention to the easily obtainable variable of total family income (number of minimum salaries earned per month). Most of the models are able to give an excellent prediction of the desired wastewater variables. Additionally, the behaviour of the main wastewater characteristics according to the hour of the day and the day of the week are analysed. Based on the results obtained, it is suggested that the classical figures of BOD concentration of 300 mg/l and per capita BOD load of S4g/inhab.d do not apply to the typical population predominant in most areas of Brazil. The actual BOD concentrations are frequently higher than 300 mg/l, while the BOD load is frequently lower than 54 g/inhab.d. The results obtained can be used for design purposes in the areas studied, and possibly in areas of similar characteristics, substituting the classical figures obtained from foreign textbooks. Copyright

Performance evaluation of UASB reactor systems with and without post-treatment.

This article evaluates and compares the actual behavior of 18 UASB reactor systems operating without (10 plants) and with (8 plants) post treatment, considering their performance and their reliability in terms of compliance with specified discharge standards. The following types of post-treatment processes were analyzed: aerated filter; anaerobic filter; trickling filter; dissolved air flotation unit; facultative pond and maturation pond. The effluent quality and the removal efficiencies were compared with typical values reported in the technical literature. A methodology developed by Niku et al. (1979) was used for the determination of the coefficients of reliability, in terms of the compliance of effluent BOD and TSS with discharge standards. The results showed that, in general, the inclusion of a post-treatment step, be it either aerobic, anaerobic or physical-chemical, can provide a substantial improvement of the effluent quality from UASB reactors in terms of BOD and TSS. In terms of the systems reliability, the actual effluent concentrations from UASB reactor followed by some post-treatment processes would meet more restrictive discharge standards than those considered in this study (60 mg L(-1) for both constituents-values prevailing in most states in Brazil).

Comparison between polishing (maturation) ponds and subsurface flow constructed wetlands (planted and unplanted) for the post-treatment of the effluent from UASB reactors.

This paper presents the results of a comparison of the performance of two treatment systems operating in parallel, with the same influent wastewater. The investigated systems are (i) UASB + three polishing ponds in series + coarse filter (200 population equivalents) and (ii) UASB + subsurface flow constructed wetlands (50 population equivalents). Two wetland units, operating in parallel, were analysed, being one planted (Typha latifolia) and the other unplanted. The systems were located in Belo Horizonte, Brazil. The wetland systems showed to be more efficient in the removal of organic matter and suspended solids, leading to good effluent BOD and COD concentrations and excellent SS concentrations. The planted wetland performed better than the unplanted unit, but the latter was also able to provide a good effluent quality. The polishing pond system was more efficient in the removal of nitrogen (ammonia) and coliforms (E. coli). Land requirements and cost considerations are presented.

Performance of a single stage vertical flow constructed wetland system treating raw domestic sewage in Brazil.

This study investigated the behaviour of two intermittently fed vertical flow constructed wetlands (one planted with Tifton 85 and the other unplanted) working in parallel, treating raw municipal sewage in Brazil for a population equivalent around 100 inhabitants. Based on a monitoring programme of over 2 years, the following items were evaluated: influence of batch frequency and the presence of Tifton 85 on the wetlands performance in terms of several physico-chemical and biological constituents. The unit with plants performed better than the one without, indicating a positive influence of the presence of plants. More attachment by total and volatile solids and larger amount of bacteria involved in the nitrogen cycle were observed in the planted filter medium, which can explain its higher nitrification and solids removal. The application of a smaller influent volume with a higher batch frequency improved the performance of both units. No signs of medium clogging have been observed in both units. The system simplicity and the good removal efficiency of organic matter, suspended solids, ammonia and helminth eggs indicate its high applicability in small communities in developing countries such as Brazil.

Performance evaluation of a novel open trickling filter for the post-treatment of anaerobic effluents from small communities.

The objective of the work is to evaluate the performance of an innovative design of a trickling filter for small population sizes, which has been implemented for the post-treatment of sanitary effluent from a UASB (upflow anaerobic sludge blanket) reactor. The unit, named open trickling filter (OTF), operates with no side walls, no perforated bottom slab and no secondary settler. The OTF packing was 3.5 m high, composed of crushed stone, with a fixed distribution system made of channels with V-notch weirs. The OTF was operated with mean surface hydraulic loading rates of 4.1 and 9.3 m³ m⁻² d⁻¹, corresponding to population equivalents of approximately 250 and 550 inhabitants, respectively. For the surface hydraulic loading rate of 4.1 m³ m⁻² d⁻¹, the median removal efficiencies obtained by the OTF and overall system (UASB + OTF) were, respectively, 24 and 83% for total suspended solids (TSS), 44 and 79% for chemical oxygen demand (COD), 42 and 82% for biochemical oxygen demand (BOD), 40 and 40% for N-ammonia. For the surface hydraulic loading rate of 9.3 m³ m⁻² d⁻¹, the median removal efficiencies obtained by the OTF and global system (UASB + OTF) were 14 and 76% for TSS, 28 and 76% for COD, 25 and 86% for BOD, 15 and 15% for N-ammonia. Considering the great simplicity, no mechanization and small footprint of the system, these results can be considered satisfactory, suggesting that the OTF is suitable for small communities, especially in developing countries.

Lognormal behaviour of untreated and treated wastewater constituents

This article presents an extensive study to select the theoretical probability distribution that represents the concentrations of major constituents from 35 wastewater treatment plants located in Brazil, as well as to verify the influence of the adopted treatment technology on the data distributions. Due to the lack of a solid basis for selecting the distributions that best fit the data, various distributions had to be tried and the choice was based on statistical tests and visual techniques, comprising a total of 3,444 tests undertaken. While comparing suitability of five distributions (normal, lognormal, gamma, exponential and rectangular) for analysis of data (influent and effluent biochemical oxygen demand, chemical oxygen demand, suspended solids, nitrogen, phosphorus, thermotolerant coliforms and flow), it was observed that the lognormal distribution was the most suitable, which is in agreement with the findings from other research studies. This conclusion requires a different position from the one currently adopted when analysing plant performance, in which symmetry of the data is generally implied, which has been shown not to be the case with the large array of data sets investigated.

Field application of a planted fixed bed reactor (PFR) for support media and rhizosphere investigation using undisturbed samples from full-scale constructed wetlands

This study presents a novel method for investigations on undisturbed samples from full-scale horizontal subsurface-flow constructed wetlands (HSSFCW). The planted fixed bed reactor (PFR), developed at the Helmholtz Center for Environmental Research (UFZ), is a universal test unit for planted soil filters that reproduces the operational conditions of a constructed wetland (CW) system in laboratory scale. The present research proposes modifications on the PFR original configuration in order to allow its operation in field conditions. A mobile device to obtain undisturbed samples from real-scale HSSFCW was also developed. The experimental setting is presented with two possible operational configurations. The first allows the removal and replacement of undisturbed samples in the CW bed for laboratory investigations, guaranteeing sample integrity with a mobile device. The second allows the continuous operation of the PFR and undisturbed samples as a fraction of the support media, reproducing the same environmental conditions outside the real-scale system. Investigations on the hydrodynamics of the adapted PFR were carried out with saline tracer tests, validating the proposed adaptation. Six adapted PFR units were installed next to full-scale HSSFCW beds and fed with interstitial liquid pumped from two regions of planted and unplanted support media. Fourteen points were monitored along the system, covering carbon fractions, nitrogen and sulfate. The results indicate the method as a promising tool for investigations on CW support media, rhizosphere and open space for studies on CW modeling, respirometry, kinetic parameters, microbial communities, redox potential and plant influence on HSSFCW.

Investigation of aerobic and anaerobic ammonium-oxidising bacteria presence in a small full-scale wastewater treatment system comprised by UASB reactor and three polishing ponds

This work applied PCR amplification method and Fluorescence in situ hybridisation (FISH) with primers and probes specific for the anammox organisms and aerobic ammonia-oxidising beta-Proteobacteria in order to detect these groups in different samples from a wastewater treatment system comprised by UASB reactor and three polishing (maturation) ponds in series. Seven primer pairs were used in order to detect Anammox bacteria. Positive results were obtained with three of them, suggesting that Anammox could be present in polishing pond sediments. However, Anammox bacteria were not detected by FISH, indicating that they were not present in sediment samples, or they could be present but below FISH detection limit. Aerobic ammonia- and nitrite-oxidising bacteria were verified in water column samples through Most Probable Number (MPN) analysis, but they were not detected in sediment samples by FISH. Ammonia removal efficiencies occurred systematically along the ponds (24, 32, and 34% for polishing pond 1, 2, and 3, respectively) but the major reaction responsible for this removal is still unclear. Some nitrification might have occurred in water samples because some nitrifying bacteria were present. Also Anammox reaction might have occurred because Anammox genes were detected in the sediments, but probably this reaction was too low to be noticed. It is important also to consider that some of the ammonia removal observed might be related to NH(3) stripping, associated with the pH increase resulting from the intensive photosynthetic activity in the ponds (mechanism under investigation). Therefore, it can be concluded that more than one mechanism (or reaction) might be involved in the ammonia removal in the polishing ponds investigated in this study.

Avaliação de desempenho de lagoa de polimento para pós-tratamento de reator anaeróbio de manta de lodo (UASB) no tratamento de águas residuárias de suinocultura

The performance of a polishing pond for treating swine wastewater from an upflow anaerobic sludge blanket (UASB) reactor was evaluated. The system was assembled with a slat settler, followed by an UASB reactor, on a real scale, and a post-treatment pond, on a demonstration scale. The following parameters were analyzed: temperature, pH, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), volatile suspended solids (VSS), total Kjedahl nitrogen (NTK), ammonia nitrogen (N-am.), organic nitrogen, total phosphorus, and total and thermotolerant coliforms. The polishing pond was highly efficient, removing an average of 58.9% of BOD, 60.1% of NTK, 57% of N-am., and 95.34% of thermotolerant coliforms.