Tilapia rearing with high rate algal pond effluent: ammonia surface loading rates and stocking densities effects.

In two pilot-scale experiments, fingerlings and juvenile of tilapia were reared in high rate algal pond (HRAP) effluent. The combination of three different total ammonia nitrogen (TAN) surface loading rates (SLR1 = 0.6, SLR2 = 1.2; SLR3 = 2.4 kg TAN·ha-1·d-1) and two fish stocking densities (D1 = 4 and D2 = 8 fish per tank) was evaluated during two 12-week experiments. Fingerlings total weight gain varied from 4.9 to 18.9 g, with the highest value (equivalent to 0.225 g·d-1) being recorded in SLR2-D1 treatment; however, high mortality (up to 67%) was recorded, probably due to sensitivity to ammonia and wide daily temperature variations. At lower water temperatures, juvenile tilapia showed no mortality, but very low weight gain. The fish rearing tanks worked as wastewater polishing units, adding the following approximate average removal figures on top of those achieved at the HRAP: 63% of total Kjeldahl nitrogen; 54% of ammonia nitrogen; 42% of total phosphorus; 37% of chemical oxygen demand; 1.1 log units of Escherichia coli.

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.

Further contributions to nitrogen removal modelling in waste stabilization ponds.

A large database from an experimental maturation pond system in Brazil was used to verify the agreement of field results with values predicted by some of the most widely accepted models to describe ammonium and total nitrogen (TN) removal in facultative and maturation ponds. The same database was used to derive a pH-independent linear model to predict ammonium removal in ponds, which was proved to be, essentially, a function of ammonium surface loading rate. In general, all these models made reasonable predictions of ammonium or TN removal but tended to overestimate low ammonium effluent concentrations while underestimating higher values of field data.

An evaluation of microbial health risks to livestock fed with wastewater-irrigated forage crops.

This paper presents the results of five experiments in which animal health risks associated with the consumption of crops irrigated with domestic wastewater were evaluated. Forage maize and Tanner grass were irrigated with treated wastewater and used in goats and calves feeding trials. The irrigated crops presented high levels of surface contamination with E. coli (10(4) -10(7) 25 g(-1) ) and salmonellae (up to 1.6 × 10(4) 25 g(-1)), but none of the animals showed signs of infection or of disease. Further, the microbiological quality of animal products always complied with the Brazilian and European Union standards for food safety. It is suggested that the WHO guideline values for restricted irrigation (≤ 10(4) E. coli 100 ml(-1) and ≤ 1 helminth egg l(-1)), which were developed to protect the health of agricultural field workers, would be equally protective of the health of both animals fed with wastewater-irrigated crops and humans consuming products from such animals.

Quantitative microbial risk assessment applied to irrigation of salad crops with waste stabilization pond effluents.

A quantitative microbial risk assessment model for estimating infection risks arising from consuming crops eaten raw that have been irrigated with effluents from stabilization ponds was constructed. A log-normal probability distribution function was fitted to a large database from a comprehensive monitoring of an experimental pond system to account for variability in Escherichia coli concentration in irrigation water. Crop contamination levels were estimated using predictive models derived from field experiments involving the irrigation of several crops with different effluent qualities. Data on daily intake of salad crops were obtained from a national survey in Brazil. Ten thousand-trial Monte Carlo simulations were used to estimate human health risks associated with the use of wastewater for irrigating low- and high-growing crops. The use of effluents containing 10(3)-10(4) E. coli per 100 ml resulted in median rotavirus infection risk of approximately 10(-3) and 10(-4) pppy when irrigating, respectively, low- and high-growing crops; the corresponding 95th percentile risk estimates were around 10(-2) in both scenarios. Sensitivity analyses revealed that variations in effluent quality, in the assumed ratios of pathogens to E. coli, and in the reduction of pathogens between harvest and consumption had great impact upon risk estimates.

UASB-polishing ponds design parameters: contributions from a pilot scale study in southeast Brazil.

This paper presents the results of five years monitoring of an experimental wastewater treatment plant in southeast Brazil, comprised of a UASB reactor followed by a submerged aerated biofilter (BF) (field scale) and shallow polishing ponds (pilot scale). Three ponds in series achieved high quality effluent standards in terms of ammonia and E.coli, but a fourth pond did not result in further efficiency. Well established models to predict ammonia and E.coli removal in facultative and/or maturation ponds were, in a way, validated for polishing ponds too. The paper also includes results of input design parameters, such as pH and E.coli die-off rate constants, and their variation along the pond series.

Post-treatment of UASB reactor effluent in waste stabilization ponds and in horizontal flow constructed wetlands: a comparative study in pilot scale in Southeast Brazil.

The results of a 20-month period study in Brazil were analyzed to compare horizontal-flow constructed wetlands (CW) and waste stabilization pond (WSP) systems in terms of land area requirements and performance to produce effluent qualities for surface water discharge, and for wastewater use in agriculture and/or aquaculture. Nitrogen, E. coli and helminth eggs were more effectively removed in WSP than in CW. It is indicated that CW and WSP require similar land areas to achieve a bacteriological effluent quality suitable for unrestricted irrigation (10(3) E. coli per 100 mL), but CW would require 2.6 times more land area than ponds to achieve quite relaxed ammonia effluent discharge standards (20 mg NH(3) L(-1)), and, by far, more land than WSP to produce an effluent complying with the WHO helminth guideline for agricultural use (< or =1 egg per litre).

Giardia spp. e Cryptosporidium spp. em água de manancial superficial de abastecimento contaminada por dejetos humano e animal / Giardia spp. and Cryptosporidium spp. in a fresh water supply source contaminated with human and animal excreta and waste water

Estudou-se ocorrência de cistos de Giardia spp. e oocistos de Cryptosporidium spp. - (oo)cistos - na bacia hidrográfica do Ribeirão São Bartolomeu, localizada no município de Viçosa, MG. O estudo incluiu as populações humana e animal existentes na área da bacia, bem como no efluente de uma estação de tratamento de esgoto (ETE) e de duas instalações para suínos. Os resultados indicam presença de (oo)cistos no manancial (médias geométricas: 3,92 e 3,62 (oo)cistos/l para Giardia spp. e Cryptosporidium spp., respectivamente). Propriedades com exploração bovina foram positivas ao longo de todo período (prevalência média de propriedades positivas 36,4 por cento para Giardia spp. e 18,0 por cento para Cryptosporidium spp.). O efluente da ETE apresentou elevada concentração de cistos de Giardia spp. (média geométrica na ordem de 10(4)/l), mas não foram encontrados oocistos de Cryptosporidium spp. A ocorrência de (oo)cistos apresentou comportamento sazonal, sendo que os valores médios de (oo)cistos e de pluviosidade do trimestre de coleta revelaram bom ajuste de correlação (R²=98,3 por cento; P=0,0087 para Giardia spp. e R²=91,8 por cento; P=0,0421 para Cryptosporidium spp.). A significativa ocorrência de (oo)cistos no manancial sugere que a forma de ocupação do solo interfere na qualidade parasitológica da água bruta. Os resultados apontam para a importância de adoção de medidas preventivas, como proteção de áreas de mananciais, objetivando reduzir riscos de transmissão de protozoários via água de consumo humano.

The occurrence of Giardia spp. cysts and Cryptosporidium spp. oocysts - (oo)cysts - was studied in a watershed (São Bartolomeu Stream-SB), at Viçosa city, MG. In the studied area, characterization of animal farms and identification of sewage and animal wastes discharges were undertaken. In addition, a sewage treatment plant (STP) and effluents of two swine farms were sampled. The results presented protozoan contamination (geometric averages: 3.92 and 3.62 (oo)cysts/l for Giardia spp. and Cryptosporidium spp., respectively). Positive cattle farms were detected during all the period, and the correspondent mean prevalences were: 36.4 percent for Giardia spp. and 18.0 percent for Cryptosporidium spp. STP effluent presented high concentration of Giardia spp. (geometric average of cysts in the order of 10(4)/l). However, Cryptosporidium spp. oocysts were not detected. The results showed that (oo)cysts concentration were influenced by climate factors. Precipitation and (oo)cysts concentration data were well correlated (R²=98.3 percent; P=0.0087 for Giardia spp. and R²=91.8 percent; P=0.0421 for Cryptosporidium spp.). Cysts and oocysts levels were remarkably high in the raw water source, pointing out the role of land use in an unprotected watershed as a source of protozoa. The results demonstrate the importance of preventive measures rather than relying on, sometimes unreliable, corrective measures such as water treatment, in order to minimize human health risks.

Wastewater irrigation of salad crops: further evidence for the evaluation of the WHO guidelines.

This paper presents the results of an experiment on salad crop irrigation with waste stabilisation pond effluents, conducted in Southeast Brazil. Over about 18 months several trials were carried out using different effluent qualities to irrigate lettuce, kale, arugula, spinach, and green pepper. Equations for predicting the bacterial quality of irrigated crops (E.coli per gram) based on the irrigation water quality (E.coli per 100 mL) were derived for low and high growing crops. The quantitative microbial risk analysis (QMRA) technique, using pathogen-ingestion scenarios based on these field data and on official statistics of vegetables consumption in Brazil, was used to estimate infection risks arising from the consumption of wastewater irrigated crops. It is inferred that irrigation with effluents complying with the WHO guidelines for unrestricted irrigation should result in salad crops acceptable for consumption.

Ammonia and phosphorus removal in polishing ponds: a case study in southeast Brazil.

Ammonia and phosphorus removal were evaluated over four years monitoring of an experimental wastewater treatment plant in Brazil: initially a UASB reactor (real scale) + three shallow polishing ponds (pilot scale), afterwards a UASB + submerged aerated biofilter (BF) (real scale) + the same pond series. Shallow ponds (h < 0.90 m) provided considerable ammonia removal, but phosphorus removal was somewhat poorer. An equation was derived for the estimation of ammonia pond effluent, based on the same assumptions of the well known Pano and Middlebrooks model. According to the experimental data, an effluent suitable for aquaculture should be achieved with retention time of 25 days.

Environmental assessment of water-courses of the Turvo Limpo River basin at the Minas Gerais State, Brazil.

A study was performed to evaluate the environmental contamination in the Turvo Limpo River basin which receives effluent discharges from domestic (residential and commercial) activities. The watercourses examined were the São Bartolomeu Stream, Turvo Sujo River, and Turvo Limpo River, located in the Minas Gerais State, Brazil. Water samples were collected at the river-side and analyzed for evaluation of pollutant inputs. The pH, temperature, electrical conductivity, redox potential (Eh), dissolved oxygen (DO), total and settleable solids, visual color, hardness, chemical oxygen demand (COD), biochemical oxygen demand (BOD), chloride, total phosphate, total nitrogen, ammonia nitrogen, nitrate, total coliforms and E. coli, as well as the Cd, Pb, Cu, and Zn speciation were determined in the watercourses. The data obtained were compared with those of the Brazilian Environmental Standards and with data from non-contaminated areas. River water characteristics in some sites were far from the limit values established for superficial waters with satisfactory quality. For instance, the BOD values reached 411 mg L(-1) for a maximum limit of 10.0 mg L(-1), while the ammonia nitrogen concentration reached 28 mg L(-1) for a maximum limit of 13.3 mg L(-1). Some sites showed E. coli values above those of non-contaminated regions. Besides the effects of sewage discharges into the water-courses, agriculture activities and the use of the area for cattle husbandry influenced the quality of the river waters, for instance, the pH of a spring-water sample reached the value of 4.3. The São Bartolomeu Stream has been contributing to the deterioration of the water quality of the Turvo Sujo River, while the Turvo Limpo River has also been affected by anthropogenic discharges in the Turvo Sujo River. The speciation of Cd, Cu and Pb showed that these metals were mainly found in the particulate fraction (i. e., associated with the suspended material). Fifty five percent of the water samples showed labile Zn concentrations greater than that of the nonlabile Zn.

Removal of E. coli and helminth eggs in UASB: Polishing pond systems in Brazil.

Ponds following anaerobic reactors, such as Upflow Anaerobic Sludge Blanket (UASB) reactors, have been termed polishing ponds in the literature. The present paper analyses the removal of E. coli and helminth eggs in five UASB-polishing pond systems in Brazil. Since there were ponds in series, the total number of ponds was 10. The ponds had average retention times varying from 2 to 21 days, and depths ranging from 0.40 to 2.00 m. The shallow ponds in series, even with low retention times, were able to produce effluents complying with the coliform WHO guidelines for unrestricted irrigation (< or = 1000 MPN/100 ml). An equation for the coliform decay coefficient was proposed: Kb (dispersed flow) = 0.710H(-0955) (20 degrees C). The equation highlights the inverse relationship between the pond depth and the decay coefficient. All polishing pond systems were able to produce effluents with helminth eggs concentrations predominantly equal to zero, and satisfying the WHO guidelines for unrestricted and restricted irrigation (< or = 1 egg/L, arithmetic mean). The approximate range of helminth eggs removal efficiency was predicted satisfactorily.