Rafael Mujeriego

Microbial indicators and pathogens: Removal, relationships and predictive capabilities in water reclamation facilities

Four water reclamation facilities in north-eastern Spain were monitored over 2 years to determine the occurrence and concentrations of a set of microbial indicators (total coliforms, Escherichia coli, enterococci, spores of sulphite reducing clostridia, somatic coliphages, F-specific RNA phages, phages infecting Bacteroides fragilis strain RYC2056 and phages infecting Bacteroides tethaiotaomicron strain GA-17), and two selected pathogens (cytopathogenic enteroviruses and viable Cryptosporidium oocysts). The indicator (survival) and index (presence) functions of the various indicators tested were evaluated through the wastewater treatments. The inactivation pattern of all groups of bacteriophages tested was closer to the inactivation of enteroviruses than to the inactivation of the conventional bacterial indicators tested. The inactivation of sulfite reducing clostridia spores and bacteriophages more closely approximates the reduction of viable Cryptosporidium than do the conventional bacterial indicators. We observed neither index functions nor a predictive relationship between any of microbial indicators and viable Cryptosporidium oocysts. In contrast, several regression models (r>0.6) and discriminant functions (67-88% well classified samples) based mostly on numbers of bacteriophages were able to predict both the presence and concentrations of enteroviruses. A combination of both bacterial and bacteriophage indicators seem to be the best choice for ensuring the microbial quality of reclaimed water.

Role of hydraulic retention time and granular medium in microbial removal in tertiary treatment reed beds

The main objective of this paper is to evaluate the role of hydraulic retention time (HRT) and granular medium in faecal coliform (FC) and somatic coliphage (SC) removal in tertiary reed beds. Experiments were carried out in a pilot plant with four parallel reed beds (horizontal subsurface flow constructed wetlands), each one containing a different type of granular medium. This pilot plant is located in a wastewater treatment plant in Montcada i Reixac, near Barcelona, in northeastern Spain. The microbial inactivation ratios obtained in the different beds are compared as a function of three selected HRTs. Secondary effluent from the wastewater treatment plant was used as the influent of the pilot system. The microbial inactivation ratio ranged between 0.1 and 2.7 log-units for FC and from 0.5 to 1.7 log-units for SC in beds with coarser granular material (5-25mm), while it ranged between 0.7 and 3.4 log-units for FC and from 0.9 to 2.6 log-units for SC in the bed with finer material (2-13mm). HRT and granular medium are both key factors in microbial removal in the tertiary reed beds. The microbial inactivation ratio rises as the HRT increases until it reaches a saturation value (in general at an HRT of 3 days). The value of the microbial inactivation ratio at the saturation level depends on the granular medium contained in the bed. The specific surface area necessary to reach 2-3 log-units of FC and SC is approximately 3m(2)/person-equivalent.

Effect of Water Depth on the Removal of Organic Matter in Horizontal Subsurface Flow Constructed Wetlands

Abstract The objective of this article is to evaluate the effect of water depth on organic matter removal efficiency in horizontal subsurface flow constructed wetlands (SSFs). Experiments were carried out in a pilot plant comprising eight parallel SSF of almost equal surface area (54–56 m2 each) and treating urban wastewater. Each SSF differs from the others in the aspect ratio or the size of the granular medium or the water depth. During a period of two years, the shallow SSFs (0.27 m water depth) removed more chemical oxygen demand (COD) (72–81%), biochemical oxygen demand (BOD)5 (72–85%), ammonia (35–56%), and dissolved reactive phosphorus (DRP) (8–23%) than deep SSFs (0.5 m water depth) (59–64% for COD; 51–57% for BOD5; 18–29% for ammonia; and 0–7% for DRP). Experiments carried out during the summer indicated that sulphate reduction accounted for a clearly higher organic matter removal in the deep SSFs than in the shallow ones. Denitrification seemed to be a significant mechanism for organic matter removal to occur in shallow SSFs. The results suggest that the relative contribution of different metabolic pathways varies with depth.

Wastewater treatment for small communities in Catalonia (Mediterranean region)

An evaluation of small wastewater treatment plants (WWTPs) treating the effluents of communities with <2000 inhabitants in Catalonia (north-east of Spain) was carried out to establish the definition of appropriate wastewater treatment (AWT) and the criteria for the selection of the alternative processes that can achieve the AWT. The implementation of an AWT in these communities before the end of the year 2005 is necessary to comply with the European Directive 91/271. The AWT is that which permits the accomplishment of quality objectives in receiving waters after the discharge of the effluents. The standards for the AWT in each particular case are set out through a contaminant loading balance. Nevertheless, the final applied standards can only be as strict as they are for larger WWTPs. These criteria are very close to those stated in the French legislation, and it is felt that they are at the same time environment-friendly and realistic for small WWTPs. Secondary treatments are generally recommended to achieve the AWT. Natural wastewater treatment systems are preferred over conventional treatments to achieve the appropriate treatment because they are simple to operate, can reach the same level of treatment efficiency and have lower operation and maintenance costs. The policy debate that has produced all these statements is described.