Disinfection kinetics of pathogens in physicochemical sludge treated with ammonia.

Ammonia is a disinfectant which can diffuse through the membrane of highly resistant structures like helminth ova. Thus, it can be considered an alternative disinfectant of wastewater sludge with high pathogenic content. In this study, the kinetic parameters of the Hom model were used to describe the inactivation with ammonia of faecal coliforms, Salmonella spp. and viable helminth ova. These were obtained in processes considering the addition of ammonia alone as well as for ammonia combined with an increase in temperature. The sludge was sampled from a municipal wastewater treatment plant using an APT (Advanced Primary Treatment) or CEP (Chemical Enhanced Primary) process. With 20% w/w of ammonia, 7 logs of faecal coliforms, 6 logs of Salmonella spp., and 83% of viable helminth ova were reduced in 2 hours contact time. To eliminate 100% of the helminth ova from samples having 88-132 ova/g TS it was needed to combine 20% of ammonia with 50 degrees C. The analysis of parameters k, n and m indicate higher resistance to inactivation of helminth ova compared to bacteria and a better performance of the ammonia process than lime stabilization to inactivate microorganisms. In addition, ammonia increased the agricultural value of the biosolids produced.     

Biological risks to food crops fertilized with Ecosan sludge.

This paper presents the microbial effects of using Ecosan sludge in agriculture. Sludge from KwaZulu Natal in South Africa having a helminth ova content of around 30 HO/gTS, faecal coliforms of 10(6) CFU/gTS, faecal streptococi of 10(6) CFU/gTS and Salmonella spp. of 10(5) CFU/gTS were applied to soils to grow carrots and spinach at different rates. Results showed that helminth ova content in crops was always greater in leaves than in stems, with a content varying from 2 to 15 HO/gTS for spinach and sludge application rates of sludge of 0-37.5 ton/ha and from 2-8 HO/gTS in carrots crops for sludge application rates varying from 0 to35 ton/ha. Health risks resulting from crop consumption were calculated using the beta-poisson and the single-hit exponential models for Salmonella and helminths eggs, respectively. For Salmonella, no risks were found when consuming carrots for all the sludge rates studied while for spinach, risks were high but results were not deemed conclusive due to the technical methods used to measure bacteria. Concerning helminths, it was found that the morbidity rate will increase by 9% for the higher sludge application rates. To increase regional risks by 1% the egg content in crops needs to be less than 0.2 HO/gTS.     

Using Ecosan sludge for crop production.

This paper presents the microbial risks associated with the reuse of Ecosan sludge in agriculture. Sludge from KwaZulu Natal Province in South Africa with a helminth ova content of 30 HO/g TS, faecal coliforms of 10(6) CFU/g TS, faecal streptococci of 10(6) CFU/g TS and Salmonella spp. of 10(5) CFU/g TS was used for this purpose. Applying different rates of sludge to spinach and carrots resulted in an increase in bacterial and helminth ova counts in crops as the quantity of sludge increased. The helminth ova content in crops was always greater in leaves than in stems, with a content varying from 2 to 15 HO/g TS for spinach with sludge application rates of 0-37.5 ton/ha and from 2-8 HO/g TS for carrot crops with sludge application rates varying from 0-35 ton/ha. Nevertheless, viability in crops was 20-25%, reducing the risk of disease. Consequently, the development of an Ecosan sludge revalorisation standard is considered important. Some recommendations are made taking into account the characteristics of the sludge as well as conditions in rural areas.     

Investigating helminth eggs and Salmonella sp. in stabilization ponds treating septage.

Sludge management arises as a relevant problem after being accumulated in primary ponds of septage treatment plants. One of the most attractive options for sludge disposal is its use in agriculture and then specific guidelines regarding hygienic quality must be fulfilled. This study aimed at evaluating the storage time needed to inactivate Ascaris eggs and Salmonella in sludge accumulated in a primary pond treating septage. Raw septage exhibited very low concentrations of viable Ascaris eggs, thus experiments with Ascaris suum eggs spiking were conducted. The concentration of Ascaris eggs in the solids accumulated at the bottom of the pond was 20 eggs/g of total solids (g TS) at the time of pond closure. Although it decreased, some eggs remained viable (0.59 mean viable eggs/g TS) up to 20 months of in-pond storage of the biosolids. Salmonella survival was studied after developing an analytical method that inhibited the native flora. Sludge was seeded with Salmonella enteritidis. An equation adequately describing Salmonella die-off in biosolids subjected to 115 days of in-pond storage/dewatering, was found to be represented by the regression: y = log MPN Salmonella/g TS = 6.67 x t(-0.086), with t = storage time elapsed in days. The initial concentration was 7.0 x 10(6) MPN/g TS and the removal efficiency was 99%.     

Helminth ova removal from wastewater for agriculture and aquaculture reuse.

In the new version of the World Health Organization (WHO), water reuse guidelines helminth ova are considered one of the main target pollutants to be removed from wastewater reuse for agriculture and aquaculture purposes. In spite of this, along with the fact that helminth ova have been considered the main health risk to wastewater reuse for agriculture for at least 20 years, relatively little research has been done to control helminth ova in the wastewater treatment field. This paper addresses (1) characteristics of helminth ova and differences with microorganisms; (2) the most frequent helminth ova genus found in wastewater; (3) helminth ova content in developed and developing countries wastewater; (4) reasons why conventional disinfection methods cannot be applied; (5) main removal mechanisms; and (6) processes that in practice have effectively removed or inactivated helminth ova.     

Bacteriological eutrophication indicators in four Colombian water bodies (South America)

For the first time in Colombia the relative abundance of Pseudomonas spp., Vibrio spp., Plesiomonas shigelloides , the Aeromonas hydrophila group, and the faecal and total coliforms were studied in three dams and a natural lagoon with a different trophic state. Coliforms were low in all the water bodies, but their number was greater in the dams with a greater anthropic activity. Vibrio spp. was not detected. The density of P. shigelloides was irregular. Pseudomonas spp. was always present and showed relatively high abundance. The bacteria of the A. hydrophila group were constant and their numbers increased with the trophic state, for which they could be indicators of the eutrophication phenomena. Significant correlation ( P < 0.05) was established between total and faecal coliforms and pH, transparency, nitrites, nitrates, and orthophosphates. P. shigelloides was correlated with faecal coliforms and Aeromonas hydrophila with total coliforms and transparency.     

Bacteriological eutrophication indicators in four Colombian water bodies (South America)

For the first time in Colombia the relative abundance of Pseudomonas spp., Vibrio spp., Plesiomonas shigelloides , the Aeromonas hydrophila group, and the faecal and total coliforms were studied in three dams and a natural lagoon with a different trophic state. Coliforms were low in all the water bodies, but their number was greater in the dams with a greater anthropic activity. Vibrio spp. was not detected. The density of P. shigelloides was irregular. Pseudomonas spp. was always present and showed relatively high abundance. The bacteria of the A. hydrophila group were constant and their numbers increased with the trophic state, for which they could be indicators of the eutrophication phenomena. Significant correlation ( P < 0.05) was established between total and faecal coliforms and pH, transparency, nitrites, nitrates, and orthophosphates. P. shigelloides was correlated with faecal coliforms and Aeromonas hydrophila with total coliforms and transparency.     

Helminth ova control in sludge: a review.

Sludge reuse for agricultural production or soil reclamation is a common practice in several countries, but it entails risks if not properly performed. One such risk is the dissemination of helminthiases diseases. As a consequence, international criteria and national standards set values to limit their content in biosolids. However, little information is available on how to inactivate helminth ova from sludge, particularly when a high content is involved as is the case in the developing world. Moreover, treatment criteria are based on a limited number of studies dealing with local characteristics that, when applied to the conditions in developing countries, produce poor results. This is because design criteria were developed for Ascaris (a kind of helminth) while sludge contains a variety of genera. In addition, much information on helminth ova was produced a long time ago using inaccurate analytical techniques. This paper summarizes research and recent technical information from the literature concerning: (a) the general characteristics of helminth ova; (b) the common helminth ova genera found in sludge; (c) the main removal and inactivation mechanisms, (d) the processes that have proven effective in practical conditions at inactivating helminth ova; and (e) analytical techniques used to enumerate these pathogens.     

Production of class A biosolids with anoxic low dose alkaline treatment and odor management.

The feasibility of full-scale anoxic disinfection of dewatered and digested sludge from Winnipeg, Manitoba with low lime doses and lagoon fly ash was investigated to determine if a class A product could be produced. Lime doses of 50 g, 100 g, and 200 g per kg of biosolids (dry) were used along with fly ash doses of 500 g, 1,000 g, and 1,500 g per kg of biosolids (dry). The mixed product was buried in eight-10 cubic metre trenches at the West End Water Pollution Control Center in Winnipeg. The trenches were backfilled with dirt and trapped to simulate anoxic conditions. Sampling cages were packed with the mixed product and pathogens non-indigenous to Winnipeg's biosolids. The cages were buried amongst the mixed biosolids in the trench. The non-indigenous pathogens spiked in the laboratory were the helminth Ascaris suum and the enteric virus reovirus. Samples were removed at days 12, 40, 69, 291, and 356 and were tested for the presence of fecal Coliform, Clostridium perfringens spores, Ascaris suum eggs, and reovirus. The pH, total solids, and free ammonia content of the mixed product were also determined for each sample. Odor was quantified for samples at both 291 and 356 days. Fecal Coliform bacteria and reovirus were completely inactivated for doses as low as 100 g lime per kg biosolids (dry) and 50 g lime + 500 g fly ash per kg biosolids (dry). Spores of the bacteria C. perfringens experienced a 4-log reduction when treated with 100 g lime per kg biosolids and a 5-log reduction when treated with doses as low as 50 g lime + 500 g fly ash per kg biosolids (dry) after 69 days. Ascaris eggs were completely inactivated in 5 gram packets for all treatments involving 100 g lime per kg biosolids (dry) after 69 days. Class A pathogen requirements were met for all treatments involving a lime dose of at least 100 g per kg biosolids. The odor potential from the produced biosolids is also assessed.     

Alum recovery and wastewater sludge stabilization with sulfuric acid.

Coagulation-flocculation is used to remove helminth ova from wastewater intended for agricultural reuse. Nevertheless, it has the drawback of producing a large amount of sludge which together with the chemicals used to treat the wastewater increases the operating cost. This can be overcome by recovering and recycling the aluminium contained in the sludge. This paper presents how an acid recovery process was applied to an Advanced Primary Treatment (APT) sludge to partially treat it and to reduce its quantity. This is a method applied several decades ago in water sludge that has not been used in secondary wastewater sludge to recover aluminium and to inactivate microorganisms. By adding sulphuric acid to a 6%TS sludge, more than 70% of the aluminium added during the coagulation flocculation process was recovered when a pH of 2 was maintained during 30 minutes and at 300 rpm of mixing conditions. This way the sludge was reduced by 45% in volume and by 63% by mass, inactivating 5 logs of faecal coliforms and 68% of helminth ova. Due to the lower alum consumption, the operating cost of the APT is reduced by 3.78 US$/1,000 m(3).     

Disinfection of sludge using lime stabilisation and pasteurisation in a small wastewater treatment plant.

Removal efficiency of faecal coliforms and helminth eggs was evaluated in a small wastewater treatment plant (WWTP) serving a population of 1,000. This system was formed by the association in series of a UASB reactor and four submerged aerated biofilters. The density of faecal coliforms and the count of helminth eggs were estimated in the liquid and solid phases of the system. Two different methods of disinfecting sludge were investigated: (a) chemical treatment with lime and (b) a physical treatment by pasteurisation. As expected, the association UASB + BF was very efficient at removal of helminth eggs from the final tertiary effluent, but coliforms were still present at high densities. Lime treatment and pasteurisation of sludge were very effective methods of disinfection and produced a sludge safe for final disposal.     

Dewatering and disinfection of aerobic and anaerobic sludge using an electrokinetic (EK) system

The objectives of the study were to upgrade sewage sludge to Class A Exceptional Quality biosolids (as defined by US EPA) using an electrokinetics dewatering system. The pathogens monitored were Salmonella spp, and fecal coliforms (FC). Ten bench-scale electrokinetic cells were set up for the disinfection of the following sludges: primary, secondary (attached growth culture and suspended culture), and anaerobically digested sludge. A conditioning liquid was also added to five cells. Blower system to aid in dewatering and drying was used in in four EK cells. Sludge characteristics such as water content, volatile solids content, sulfate and chloride ions concentrations, FC and Salmonella spp. before and after the tests were monitored. The highest total solids content (98% TS) was achieved in the cell with the low voltage gradient, in the presence of the conditioner and with the blower system. An average reduction by 50% of volatile solids was observed. The highest, 11 log-reduction of Salmonella spp. was observed in a cell with anaerobically digested sludge. No fecal coliforms were observed in any of the cells after EK treatment.     

The reuse of treated wastewater for agricultural purposes in Nicaragua; Central America.

The first subsurface flow wetland (SSFW) system for about 1,000 PE, was constructed in Nicaragua in 1996 to apply this technology in the form of an integral project, combining the treatment of domestic wastewater with its reuse for crop production in small and medium size communities. The SSFW-effluent meets all standards established in the national regulations for wastewater reuse in agriculture, except for faecal coliforms, existent at an average concentration of 7 x 10(4) MPN/100 ml. A conventional surface irrigation method was used to irrigate different crop species selected to establish their risk of contamination. To judge the potential health risk for consumers and farmers, samples of vegetables and fruits harvested in the dry seasons of the years 1997 to 2002, were analyzed for the presence of pathogenic microorganisms like faecal coliforms, salmonella and shigella. In addition, a yield comparison between crops irrigated with well water using chemical fertilizers, and crops irrigated with the effluent of the SSFW-system was made, to analyze the economical benefits of the wastewater reuse.     

Subsurface constructed wetlands for wastewater treatment and reuse in agriculture: five years of experiences in Sicily, Italy.

The paper reports the results of an investigation on a H-SSF constructed wetland for tertiary treatment in a small community located in eastern Sicily, Italy. The system is designed to reuse wastewater for the irrigation of olive orchards covering about 150 hectares. From March 2001 to September 2005, wastewater samples were collected and the following chemical-physical parameters were determined according to Standard Methods: temperature, pH, EC, DO, TSS (105degrees C), BOD5, COD, TN, TP. The following microbiological parameters were also evaluated: total coliforms, faecal coliforms, Escherichia coli, faecal streptococci, Salmonella, helminth eggs. Mean removal efficiencies ranged from 77 to 92% (TSS), 37 to 72% (BOD5), 51 to 79% (COD), 97 to 99.5% (E. coli). Removal efficiency of Salmonella and helminth eggs was always 100% in all samples; however, only 150% of total samples matched the limit of E. coli (< 50 CFU/100 mL) fixed by Italian legislation for wastewater reuse.     

Removal of contaminants and pathogens from secondary effluents using intermittent sand filters

Intermittent infiltration percolation of wastewater through unsaturated sand bed is an extensive treatment technique aimed at eliminating organic matter, oxidizing ammonium and removing pathogens. The main purpose of this study was to determine the depuration efficiencies of a sand filter to remove contaminants from secondary wastewater effluents. Elimination of pathogenic bacteria (total and faecal coliforms, streptococci) and their relationship with the filter depth were investigated. Results showed a high capacity of infiltration percolation process to treat secondary effluents. Total elimination of suspended solids was obtained. Mean removal rate of BOD(5) and COD was more than 97 and more than 81%, respectively. Other water quality parameters such as NH(4)-N, TKN and PO(4)-P showed significant reduction except NO(3)-N which increased significantly in the filtered water. Efficiency of pathogenic bacteria removal was shown to mainly depend on the filter depth. Average reductions of 2.35 log total coliforms, 2.47 log faecal coliforms and 2.11 log faecal streptococci were obtained. The experimental study has shown the influence of the temperature on the output purification of infiltration percolation process.     

Microbiological quality of groundwater sources used by rural communities in Limpopo Province, South Africa.

A survey of the microbiological quality of water from 194 boreholes (97 privately owned and 97 communal boreholes) in the rural Thitale-Hlanganani area of the Limpopo Province, South Africa was carried out between August 2002 and August 2003. Very little information on the microbiological quality of privately-owned boreholes in rural communities is available raising concerns about the safety of these groundwater supplies. In this study, levels of total coliforms, thermotolerant (faecal) coliforms, faecal enterococci, Clostridium perfringens (vegetative cells and spores) and somatic coliphages were determined for community and privately-owned borehole water. The average counts for total coliforms, faecal coliforms, faecal enterococci and Clostridium perfringens exceeded the South African recommended guideline limits of 0-10 counts.100 ml(-1) for total coliforms and 0 counts. 100 ml(-1) for faecal coliforms, faecal enterococci and Clostridium perfringens respectively. Comparisons between the levels of indicator bacteria present in private and communal boreholes during dry seasons indicated a statistical difference for faecal enterococci bacteria (p = 0.005) and Clostridium perfringens (p = 0.08). Comparisons between the levels of indicator bacteria present in private and communal boreholes during rainy seasons indicated statistical differences between total coliforms (p = 0.05), faecal coliforms (p = 0.03) and Clostridium perfringens (p = 0.009) bacteria. No significant differences in the presence of somatic coliphages in both private and communal borehole water were see. The results indicated the need for environmental impact assessment studies to monitor the microbiological quality of groundwater sources in rural communities.     

Characteristics of indicator microorganisms in paddy rice plots after reclaimed water irrigation.

A study was performed to examine the effects of reclaimed-water irrigation on microorganism concentration in the ponded-water of paddy rice plots. Several treatments were used and each one was triplicated to evaluate the change of indicator microorganisms (total coliforms (TC), faecal coliforms (FC), and E. coli) concentrations in 2003 and 2004 growing seasons. Their concentrations increased significantly after irrigation, but decreased by approximately 45% in 24 h. It implies that agricultural activities such as ploughing and fertilising need to be practiced one or two days after irrigation, considering health risks. Treatments with UV-disinfected water irrigation, demonstrated significantly lower concentrations than others, including control plots where natural water was irrigated. The monitoring result from actual paddy rice fields and experimental paddy plots showed that concentrations of indicator microorganisms ranged from 10(2) to 10(5) MPN/100 mL. The field scale water reuse research project is in progress and national guidelines for reclaimed-water irrigation are under preparation in Korea. A comprehensive assessment of existing agricultural practices and a thorough monitoring in the fields as well as treatment plots are recommended to make national guidelines more representative.     

Pathogen removal efficiency from UASB + BF effluent using conventional and UV post-treatment systems.

The aim of this study was to verify the efficiency of removal of microorganisms in effluents of a Wastewater Treatment Plant (WWTP) comprising an association of a UASB reactor followed by three submerged aerated biofilters (BAF) and one tertiary filter. The WWTP designed to treat domestic wastewater from a population of 1,000 inhabitants showed high removal efficiency for organic matter and suspended solids. Helminth eggs were also efficiently removed from the tertiary effluent and were found in the sludge from the UASB reactor; however, removal of bacteria in this system was very low. To enhance the efficiency of the system, the effluent from tertiary filters was submitted to UV disinfection in a real scale reactor. Our results showed that UV irradiation was very effective at lowering the concentrations of E. coli, thermotolerant coliforms and coliphages to acceptable levels for agricultural reuse. Salmonella spp. and helminth eggs were seeded into the tertiary effluent before passing through the UV reactor. Salmonella was not found in the final effluent, but helminth eggs were not completely inactivated by UV irradiation and viable eggs were detected after 28 d of incubation.     

Combining UASB and the "fourth generation" down-flow hanging sponge reactor for municipal wastewater treatment.

A "fourth generation" down-flow hanging sponge (DHS) Reactor has been developed and proposed as an improved variant of post-treatment system for UASB treating domestic wastewater. This paper evaluates the potential of the proposed combination of UASB and DHS as a sewage treatment system, especially for developing countries. A pilot-scale UASB (1.15 m3) and DHS (0.38 m3; volume of sponge) was installed in a municipal sewage treatment site and constantly monitored for 2 years. UASB was operated at an HRT of 6 h corresponding to an organic load of 2.15 kg-COD/m3 per day. Subsequently, the organic load in DHS was 2.35 kg-COD/m3 per day, operated at an HRT of 2 h. Organic removal by the whole system was satisfactory, accomplishing 96% of unfiltered BOD removal and 91% of unfiltered COD removal. However, nitrification decreased from 56% during the startup period to 28% afterwards. Investigation on DHS sludge was made by quantifying it and evaluating oxygen uptake rates with various substrates. Average concentration of trapped biomass was 26 g-VSS/L of sponge volume, increasing the SRT of the system to 100-125 d. Removal of coliforms obtained was 3-4 log10 with the final count of 10(3) to 10(4) MPN/100 ml in DHS effluent.     

Evaluation of phytotoxic elements, trace elements and nutrients in a standardized crop plant, irrigated with raw wastewater treated by APT and ozone.

This project studied the benefits of applying Advanced Primary Treatment (APT) and ozone (O3) to raw wastewater destined for reuse in agriculture. The ozone was applied directly to raw wastewater, as well as to wastewater already treated with APT, and the results compared against a control sample of potable water. The experimental conditions that reported the best results was wastewater treated with O3 (at a dose of 4.8 mg/L, at pH 7, temperature 23 degrees C, for 1 hr), given that it met standards in force in Mexico with regard to micro-organism and heavy metal content. Under these conditions, after 15 min of ozonation, 100% destruction of the following bacteria was observed: V. cholerae, S. typhi as well as total and faecal coliforms. Destruction of helminth eggs and Giardia sp. took one hour. No phytotoxic elements or heavy metals were found. The balance of nutrients N:P:K (300:100:200 mg/kg) required for lettuce growth, was found in wastewater subjected to both treatment plans. However, ozone favoured the nitrification and assimilation of the nutrients, by contributing oxygen to the soil. Therefore, these conditions produced the greatest lettuce growth, the entire plant averaging 38 cm in length and 125 g. in weight. Moreover, a better appearance of the leaves was also noted.