Observações sobre o desempenho das ETE's de Campina Grande e Monteiro (PB).

Abstract

This present research was carried out in two waste stabilization ponds (WSP) systems treating domestic sewage, located in Campina Grande and Monteiro municipalities (Paraiba State - Brazil), with the aim to evaluate their performance using data from systematic monitoring programs of physical, chemical, biological and microbiological parameters. Samples of raw sewage (RS) and final effluent (FE) were collected monthly from aug/2000 to aug/2001and analyzed for: temperature, pH, electric conductivity, sodium, potassium, chlorides, dissolved oxygen (DO), BOD, COD, total and suspended solids and and their fractions, ammonia, total and soluble phosphorous and faecal coliforms. Also helminth eggs and algae biomass (chlorophyll "a") were quantified. The results of BODS and COD classified the raw sewage of both WSP systems as medium and strong concentration, respectively. The results showed that some parameters were not removed significantly along the treatment systems and among those parameters stood out: volatile total solids (-135; 84%) and the total phosphorus (-116; 37%) in Campina Grande WSP. In Monteiro WSP, it can stand out the following parameters: DQO (-227; 95%), total suspended solids (-319; 84%), fixed suspended solids (-700; 88%), volatile suspended solids (-251; 93%) and total phosphorus (-300; 90%) that didn't suffer removal in the period, but an increment in concentration in the final effluent.. This absence of removal can be attributed to the expressive fluctuations of some parameters, particularly in the final effluent. The results submitted to anstatistical analysis (test-t) showed that macronutrients of P and N in RS and FE of Monteiro's WSP did not present significant differences for mean values of total phosphorous and ammonia, revealing low removal (average of 17%). The mean effluent concentration of ammonia was high (55,7 mg/1), above the maximum values allowed by CONAMA resolution 20/86 for release in receiving water body. In Campina Grande WSP the ammoniacal nitrogen concentration also surpassed those limits, although the removal was of 42%. The mean values of RS and FE did not differ to each other significantly. In these two WSP systems the mean concentrations of FC in raw sewage and final effluent presented significant differences with reduction of 99,55% and 92,82% in the final effluent in Campina Grande WSP and Monteiro WSP, respectively. Although Monteiro's system did not produced an effluent with appropriate bacteriological quality (remancesnte of 2,0 x 106 CF\100mi) according to the expected waste stabilization pond configuration (serie of anaerobic followed by facultative). Campina Grande WSP system produced a final effluent with up to 105CFU/100ml, appropriate for cultures class B ( cereal crops, industrial crops, fodder crops, pasture and trees) accordingly to the World Health Organization. Both WSP removed all helmint eggs from in the raw sewage. Monteiro's WSP system stood out for the excellent removal of soluble orthophosphate, with a mean value of 65%, associated whit the exuberant growth of the cyanobacteria Microcystis spp. However the presence of this cyanobacteria could be represent a new inconvenience for the final effluent quality at least theoretically, since they could contribute with the presence of toxins in the receiving water body.