A. Soler

Nutrient removal and sludge production in the coagulation-flocculation process.

Nutrient removal and sludge production in the coagulation-flocculation process, applied to a slaughterhouse effluent, have been studied. Fe2(SO4)3, Al2(SO4)3 and polyaluminium chloride were used as coagulants. Inorganic products were used as coagulant aids: activated silica, powdered activated carbon and precipitated calcium carbonate and synthetic polyelectrolytes: cationic polyacrylamide, polyacrilic acid, anionic polyacrylamide and polyvinyl alcohol. Performances were measured under optimum conditions for the products used. They were found after studying the different variables which influence the process. Phosphorus removal is very high (approximately 100% for the orthophosphate and between 98.93% and 99.90% for the total phosphorus). Ammonia nitrogen removal is very low although appreciable performances are observed for albuminoid nitrogen (73.9-88.77%). The use of coagulant aids reduces the volume of the sludge produced up to 41.6%.

Microscopic observation of particle reduction in slaughterhouse wastewater by coagulation-flocculation using ferric sulphate as coagulant and different coagulant aids.

A coagulation-flocculation treatment has been applied to a slaughterhouse liquid effluent, using ferric sulphate as coagulant and activated silica, powdered activated carbon, cationic polyacrylamide, polyvinyl alcohol, polyacrylic acid and anionic polyacrylamide as coagulant aids in order to improve the settling time. Once the optimal conditions had been established (speed and time of stirring during flocculation step, pH, coagulant and coagulant aid doses), the efficiency of the coagulation-flocculation process was studied by comparing the particle size distribution before and after the addition of the coagulant. When ferric sulphate was used without the coagulant aids, particle removal efficiency varied with size, although overall efficiency was quite substantial (87%). The use of coagulant aids improved the removal efficiency, except in the case of activated silica, when it fell to 78%. In all other cases removal efficiency values between 93% (for polyvinyl alcohol) and 99% (for anionic polyacrylamide) were reached.

Hydraulic performance of a deep wastewater stabilization pond

Abstract The hydraulic performance of a deep wastewater stabilization pond located in the Espinardo Campus of the University of Murcia was studied. The pond has a maximum capacity of 15,000 m3, with a maximum depth of 8 m. Sulforhodamine B dye is used as a tracer in the experimental study, which was carried out in two different climatic periods, winter and summer, so that the influence of temperature on the internal hydrodynamic of the lagoon could be ascertained. Two types of sample were obtained. One was taken from the mass of water within the pond and the other at the outlet. The mean real residence time ( t ) was calculated and it was below the spatial time (τ) both in summer and winter. Sampling carried out in the outlet flow along the time allowed the application of population balance models and to analyze the existence of short circuits and dead spaces. The pond active volume was calculated, being 70 and 22% of total volume in winter and summer, respectively. In both seasons, the active zone showed a hydrodynamic behaviour similar to the completely mixed continuous tank reactor (observed in the curves C and in the fitting of the experimental data at outlet and the use of the combined model of Cholette and Cloutier). From the experimental data of the remaining BOD5 it was possible to calculate the global kinetic constants for organic matter degradation and, from this, the constants at 20°C obtained at the most unfavourable (higher) water temperature observed. Both in winter and summer constants values (k20 = 0.46 and 0.32 d−1) seemed to point to the active zone of the system, showing a fundamentally aerobic behaviour.

Influence of thermal stratification on the behaviour of a deep wastewater stabilization pond

Abstract Deep lagooning is an alternative to conventional lagooning and it implies smaller land requirements as an additional advantage. Treatment in deep wastewater stabilization ponds is influenced by thermal stratification. The object of this paper is the study, over a 1-yr period (October 1986–December 1987), of the influence of temperature on the behaviour of a treatment unit (an 8 m deep pond) which receives domestic wastewater. For this study, a spatiotemporal follow-up of the natural treatment process has been conducted. The removal efficiencies achieved for the following parameters varied as follows: COD, 71–92%; BOD5, 83–97%; total Kjeldahl nitrogen, 51–98.8%; ammonia nitrogen, 38.8–99.9%; total phosphorus, 42.2–92.9% and orthophosphate, 40–99%. Log reduction of microorganisms varied between 2.0 and 3.0 for total coliforms, 1.1–3.0 for faecal coliforms and 1.7–3.3 for faecal streptococcus. Other physicochemical parameters observed were: temperature, dissolved oxygen, pH, nitrates and nitrites. The continuous flow of wastewater did not hinder the appearance of a marked stratification in spring-summer: an aerobic epilimnetic zone and an anaerobic hypolimnetic one remained clearly differentiated. The evolution of all the parameters observed was similar. In the absence of thermal stratification, the system was found to function in approximately complete mixing conditions, and the value of each parameter was almost constant throughout the water column; nevertheless, the presence of stratification caused a vertical distribution with marked gradients in the thermocline zone.

Primary productivity in a deep sewage stabilization Lagoon

Primary productivity and production measurements and their relationship to observed variations in the concentrations of nutrients (N and P), CO2, pH, temperature, dissolved oxygen and solar radiation were studied in an 8 m deep sewage stabilization pond from October 1986 to December 1987. Two types of tests were carried out: short-term and long-term. The latter permitted the transformation of short-term measurements into daily measurements and the obtention of the relationship between the time of day and primary production. The measurement of primary production was performed using the 14C technique. The highest primary productivity values were detected during the spring-summer period, which was characterized by high temperatures and an increased degree of solar radiation. The maximum value was obtained during June (14.38 mg C mg Chl−1 day−1) and was accompanied by: (a) a decrease in the concentration of nutrients (N and P) and CO2, (b) an increase in pH levels and dissolved oxygen concentrations and (c) a significant proliferation of cyanobacteria (which indicated a low organic loading).

Determination of low concentration of sulphorhodamine B in wastewaters and stabilization ponds

Abstract The use of sulphorhodamine B, a known red fluorescent dye as a quantitative tracer in hydrological studies related to wastewaters has been proved experimentally. The interference in the accuracy of fluorescence readings owing to dissolved or suspended contaminants in wastewaters, especially at low concentrations of dye, was solved by successive filtering and eluting of the sample through a sep-pack C-18. The sulphorhodamine B, which is concentrated by displacement with small volumes of methanol, was thus retained. Volumes were then read with an fluorescence spectrophotometer. The procedure was demonstrated to be valid for use with sewers, stabilization ponds and wastewaters for concentrations as low as 5 × 10 −7 g litre −1 .