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.

Trihalomethane occurrence in chlorinated reclaimed water at full-scale wastewater treatment plants in NE Spain.

Total trihalomethane (TTHM) concentrations were determined in three chlorinated effluents (i.e. secondary and tertiary) from full-scale wastewater treatment plants (WWTP) in NE Spain over a 2-year monitoring period (May 2003-February 2005). Low TTHM concentrations (2-30 microg L(-1)), according to international standards for drinking water (80-150 microg L(-1)), were obtained in all samples analysed. The effects of (a) ammonia nitrogen and bromide concentrations, (b) UV light exposure, (c) tank storage, and (d) water temperature were evaluated. Two chlorination strategies were adopted: low chlorine dosages (2-5 mg Cl2 L(-1)) and a high-chlorine dosage (16 mg Cl2 L(-1)). The effects of storing chlorinated reclaimed water and of UV light exposure before chlorination were also evaluated. Samples collected over the 2-year monitoring period offered the possibility to assess the numerous variables affecting THM formation. A statistical evaluation of Platja d'Aro WWTP data set shows a low TTHM formation in the presence of high ammonia nitrogen concentration (p<0.05). That result can be attributed to the formation of chloramines by reaction with added chlorine, at doses below breakpoint chlorination. An increase in TTHM concentration in the presence of bromide (0-1 mg L(-1)) was also recorded (p<0.05). In contrast to published reports, TOC had a negative effect on TTHM formation. COD and turbidity had no statistical significance on TTHM formation. As expected, chlorination promoted TTHM formation in the three water reclamation plants monitored. Nevertheless, no statistical difference was observed when chlorinated effluents were kept in storage tanks. Exposure to UV light did not affect either formation or removal of TTHM. The relative production of TTHM during warm and cold seasons was also evaluated. TTHM production decreased with higher temperatures, but that could be attributed to the increase of ammonia nitrogen concentration observed during the warm summer seasons.

Effect of water depth on the removal of organic matter in horizontal subsurface flow constructed wetlands.

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.

Effect of design parameters in horizontal flow constructed wetland on the behaviour of volatile fatty acids and volatile alkylsulfides.

A pilot-scale horizontal flow constructed wetland (HFCW) system planted with common reed (Phragmites sp.) was constructed to study how hydraulic loading rate (HLR), aspect ratio, water depth, and granular medium affect to the fate of several organic matter degradation intermediates namely, acetic acid (HAc), isovaleric acid (Isoval), and dimethylsulfide (DMS). ANOVA statistical analysis performed on the data set of 8 months of operation shows that the HLR and the water depth are two major factors that control the performance of HFCWs for the target analytes. A clear difference in the HFCW effluent concentrations was obtained according to water depth. Effluents of the shallow water depth contained lower DMS (1.05-1.44 microg l-1), HAc (7.91-10.9 mg l-1), and Isoval (0.11-0.15 mg l-1) concentrations than the deeper beds (DMS: 1.68-2.40 microg l-1; HAc: 9.29-14.4 mg l-1, and Isoval: 0.20-0.31 mg l-1). Such differences could be accounted to the different formation and consumption rates of the organic matter degradation intermediates, which is related with the redox potentials (E). Indeed, it could lead to different biochemical reactions of organic matter degradation according with the E value. HLR has a statistically significant influence on the effluent HAc, Isoval, and DMS concentrations. Seasonal variability of effluent HAc concentration shows that it is independent on the HAc loading. While the loading showed no seasonal pattern, the removal efficiency was clearly higher in cold months, which suggests a predominant internal production of HAc in HFCWs in the warm season from the accumulated organic particulate matter. Similar results were also found when Isoval and DMS were considered.

Factors affecting linear alkylbenzene sulfonates removal in subsurface flow constructed wetlands.

The behavior of linear alkylbenzene sulfonate (LAS) and sulfophenyl carboxylate (SPC) biointermediates in a pilot subsurface flow constructed wetland (SFCW) is reported for the first time. The effects of wetland configuration and operation on their treatment efficiency were investigated. The pilot SFCW constituted by eight beds of 55 m2 with different aspect ratios (1 x 1; 1.5 x 1; 2 x 1; 2.5 x 1), two water depths (i.e., 0.47 and 0.27 cm) at 5 cm below surface and two medium sizes (i.e., D60 = 10 mm and 3.5 mm) planted with Phragmites sp. That SFCW pilottreats urban wastewater (i.e., 200 inhabitants) and was operated at four hydraulic loading rates (HLRs) (20, 27, 36, and 45 mm d(-1)). Influent and effluent sampling was carried out from May 2001 to January 2002 with a weekly pattern. Main results were as follows: (i) water depth has a major influence on the performance of SFCW for the LAS removal, and HLR shows significant effect on SPC evolution; (ii) water temperature has a significant effect on the LAS evolution; (iii) biodegradation of LAS and SPC can occur under sulfate-reducing environment and mixed conditions (i.e., sulfate-reducing and denitrification), but aerobic respiration cannot be excluded; and (iv) C13 LAS homologues were generally removed in higher extent than the shorter alkyl chain counterparts. In the most appropriate conditions, LAS and SPC can be biodegraded up to 71% and 11%, respectively, in the pilot SFCW evaluated.

Initial contaminant removal performance factors in horizontal flow reed beds used for treating urban wastewater.

This study evaluates the effect of hydraulic loading rate (HLR), aspect ratio, granular medium size and water depth on the removal of selected contaminants during the start up of horizontal subsurface flow reed beds (HFRBs). Experiments were carried out in a pilot-scale HFRB system comprising four pairs of lined beds of almost equal surface area (54-56 m(2) each bed), with the following aspect ratios: 1:1, 1.5:1, 2:1 and 2.5:1. The size of the granular medium of each pair varied from coarse granitic gravel ( D(60) = 10mm, C(u) = 1.6) to small granitic gravel (D(60) = 3.5 mm, C(u) = 1.7). The beds of the pair with longest aspect ratio were made shallower (0.27 m) than the rest (0.5m) The system was sampled weekly from May 2001 to January 2002. The results indicate that HLR and water depth are determining factors in the performance of the HFRBs. Beds with a water depth of 0.27 m removed more COD (70-80%), BOD(5) (70-85%), ammonia (40-50%) and dissolved reactive phosphorus (DRP) (10-22%) than beds with a depth of 0.5m (60-65% for COD, 50-60% for BOD(5), 25-30% for ammonia, and 2-10% for DRP). The higher efficiency observed shallower beds was related to their less reducing conditions (average redox potential (E) ranging from -351 to -338 mV) than beds with a depth of 0.5m (-390 to -358 mV). The difference in E status between two bed types seems to lead to differences in the biochemical processes. In fact, denitrification was estimated to be a significant reaction in shallower beds.

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.