Chapter Two Water Quality Considerations

1. Chapter TwoWater Quality Considerations

2. INTRODUCTION Water quality is the most important issue in water reuse systems that determines the acceptability and safety of the use of recycled water for a given reuse application. For each category of water reuse, the definition of appropriate water quality is driven by a number of health, safety, sociopsychological, and technical economic criteria (Figure 2.1).

4. INTRODUCTION As a rule, water quality objectives are set by guidelines and regulations, which in turn determine the treatment technology to be used. Table 2.1 shows the list of parameters used in the evaluation of water quality for irrigation (the most important parameters are given in bold).

6. INTRODUCTION The typical concentrations in raw municipal wastewater and the main characteristics and impacts of these parameters for water reuse are given in Table 2.2. Of the four categories, microbiological parameters have received the most attention. Since monitoring for all pathogens is not realistic, specific target organisms such as fecal or total coliforms are being used as indicators of potential health risk.

9. INTRODUCTION In addition, other parameters are chosen and used for regulatory purposes and to monitor the treatment efficiency of a process or before reuse, depending on the type of reuse or regional specificities. For example, water salinity is of great concern in agricultural reuse, while trace organics are of lesser concern for agricultural reuse but are an important issue for potable reuse.

10. INTRODUCTION Wastewater quality data routinely measured and reported are mostly in terms of general parameters (e.g., biochemical oxygen demand [BOD5 ], suspended solids [SS], chemical oxygen demand [COD], which are of interest in water pollution control in receiving water bodies. While monitoring of suspended solids can be useful to predict clogging problems in irrigation systems, COD and BOD5 usually are not directly used in irrigation project planning, although organic constituents can be problematic if present in high concentrations.

11. INTRODUCTION The evaluation of nutrient content of wastewater (N and P) is becoming increasingly important to avoid eutrophication, as well as to assess the fertilizing value of these waters.

12. INTRODUCTION The main factors that affect recycled water quality include: source control, type of sewage system, wastewater treatment and operation, and storage and distribution

13. PARAMETERS WITH HEALTH SIGNIFICANCE Biological risks related to water reuse have been recognized since the very beginning of irrigation with wastewater. On the other hand, the considerationsrelated to chemical risks have been developed recently following improvements in analytical capabilities. Additionally, biological risks have a relatively immediate outcome (illnesses develop in a short period of time), while chemical risks are translated into time-delayedillnesses (carcinogens, long-term toxicity, etc.).

14. PARAMETERS WITH HEALTH SIGNIFICANCE1. Chemicals Human health-related issues involving toxic chemicals have been reported only for irrigation with wastewater heavily polluted by industrial wastedischarge. Municipal wastewater that has limited industrial wastewater input generally contains concentrations of organic and inorganic compounds that do not present health concerns when the recycled water is used for irrigation.

15. PARAMETERS WITH HEALTH SIGNIFICANCE1. Chemicals The principal health hazards associated with chemical constituents of recycled water arise from the contamination of crops or groundwater by the following compounds: Cumulative poisons, principally trace elements (heavy metals). Carcinogens, mainly organic chemicals.

16. PARAMETERS WITH HEALTH SIGNIFICANCE1. Chemicals Pharmaceuticals (antibiotics, synthetic drugs) and personal care products. Other compounds suspected to exert endocrine disruption properties (hormones or other chemicals such as PCBs, octilphenol, nonilphenol, etc.)

17. PARAMETERS WITH HEALTH SIGNIFICANCE1. Chemicals During the last 10 years, an impressive improvement in analytical capacity has led to the discovery in natural waters of a huge amount of substances capable of exerting negative effects on humans. Health-related concerns (endocrine disruption, feminization of fishes, antibiotic resistance of pathogens, etc.) pertaining to endocrine disruptors, pharmaceuticals, and personal care products in raw wastewater, recycled water, and other waters are receiving increased attention, as is the removal of these constituents during wastewater treatment and soil percolation.

18. PARAMETERS WITH HEALTH SIGNIFICANCE1. Chemicals This is currently a fertile field for research, because such compounds enter the water cycle through wastewater disposal. This knowledge creates an additional motivation to find treatments to eliminate such substances, which are usually present in very low concentrations.

19. PARAMETERS WITH HEALTH SIGNIFICANCE2. Pathogens The greatest health concern when using recycled water for irrigation is related to pathogens that could be present. It is widely known that it is not practical to establish the presence or absence of all pathogenic organisms in wastewater or recycled water in a timely fashion. For this reason, the indicator organism concept was established many years ago to allow monitoring of a limited number of microbiological constituents.

20. PARAMETERS WITH HEALTH SIGNIFICANCE2. Pathogens Table 2.3 enumerates the microbiological organisms (pathogens and indicator organisms) that are usually analyzed for to establish the presence or absence of health hazards. Table 2.4 provides the survival time of some common pathogens under different conditions in fresh water, sludge, soil, and crops.

24. PARAMETERS WITH HEALTH SIGNIFICANCE2. Pathogens Epidemiological studies conducted to date have not established definitive adverse health impacts attributable to the use of appropriately treated recycledwater for irrigation. Nevertheless, there is clear epidemiological evidenceof health problems when raw or improperly treated wastewater is used for irrigation in areas where such infections are endemic. Table 2.5 summarizes the findings of some of these studies.

26. PARAMETERS WITH HEALTH SIGNIFICANCE2. Pathogens Adverse health effects have been detected only in association with the use of raw or poorly settled wastewater, while inconclusive evidence suggested that appropriate wastewater treatment could provide a high level of health protection. Natural barriers also reduce the threat of crop contamination by pathogens. Cell walls of plant roots and leaves filter the irrigation water, and microorganisms cannot readily pass through and into the edible tissues of the crops unless the cell walls are injured.

27. PARAMETERS WITH HEALTH SIGNIFICANCE2. Pathogens Moreover, drying and solar radiation further prevent any organisms remaining in irrigation water from continuing to be viable on plant surfaces as long as there is an adequate drying period after the last irrigation and before harvest. These mechanisms normally provide a high level of natural protection against contamination of food crops from many pathogens that might be present in recycled water.

28. PARAMETERS WITH HEALTH SIGNIFICANCE2. Pathogens Potential risks induced by the presence of pathogenic microorganisms in wastewater or on crops may become actual risks if the following four criteria occur: The pathogen must reach the plant or be able to multiply to the number required for an infective dose. A human host must come into contact with the infective dose of the pathogen. The host must become infected. Disease results from the infection or leads to further transmission.

29. PARAMETERS WITH AGRONOMIC SIGNIFICANCE Important agricultural water quality parameters include a number of specific properties of water that are relevant in relation to the: yield and quality of crops, maintenance of soil productivity, and protection of the environment.

30. PARAMETERS WITH AGRONOMIC SIGNIFICANCE The quality of irrigation water is of particular importance in arid zones where extremes of temperature and low relative humidity result in high rates of evaporation with consequent deposition of salt, which tends to accumulate in the soil profile.

31. PARAMETERS WITH AGRONOMIC SIGNIFICANCE The physical and mechanical properties of the soil, such as soil structure (stability of aggregates) and permeability, are very sensitive to the type of exchangeable ions present in irrigation water. Thus, when water reuse is being planned, several factors related to soil properties must be taken into consideration.

32. PARAMETERS WITH AGRONOMIC SIGNIFICANCE1. Salinity Compared to many other irrigation waters, recycled water generally has a low to medium salinity with electrical conductivity of 0.6 to 1.7 dS/m. Some dissolved mineral salts are identified as nutrients and are beneficial for plant growth, while others may be phytotoxic or may become so at high concentrations.

33. PARAMETERS WITH AGRONOMIC SIGNIFICANCE1. Salinity The major salinity sources in recycled water are: drinking water (especially hardness and naturally occurring salts), salts added by urban or industrial water use, infiltration of brackish water into sewers, and agricultural irrigation (impact on groundwater salinity).

34. PARAMETERS WITH AGRONOMIC SIGNIFICANCE1. Salinity Salinity in the soil is related to, and often determined by, the salinity of irrigation water. The rate at which salts accumulate to undesirable levels in soils depends on the following factors: Their concentration in the irrigation water The amount of water applied annually Annual precipitation Evapotranspiration Soil characteristics, both physical and chemical

35. PARAMETERS WITH AGRONOMIC SIGNIFICANCE1. Salinity Dissolved salts increase the osmotic pressure of soil water and consequently lead to an increase in the energy plants must expend to take up water from the soil. As a result, respiration is increased and the growth and yield of most plants decline progressively as osmotic pressure increases.

36. PARAMETERS WITH AGRONOMIC SIGNIFICANCE1. Salinity Water salinity can be reported either as total dissolved solids (TDS, mg/L) or as electrical conductivity (ECw ), measured in mmhos/cm or most correctly in dS/m. The relationship between ECw and TDS is approximately ECw (dS/m)× 640= TDS (mg/L). The symbol ECe is used to designate the electrical conductivity of the soil saturation extract.

37. PARAMETERS WITH AGRONOMIC SIGNIFICANCE1. Salinity Recently, the classification of saline water has been reconsidered (Table 2.6) on the basis of research and practical observations. This classification must be used only as a guideline to determine the level of salinity of irrigation waters. It is important to stress that Table 2.6 cannot be used to assess the suitability of saline water for irrigation, because a number of other conditions must be taken into account, including crop, climate, soil, irrigation method, and management practices

39. PARAMETERS WITH AGRONOMIC SIGNIFICANCE2. Toxic Ions Many of the ions that are harmless or even beneficial at relatively low concentrations may become toxic to plants at high concentration This effect could result either from: direct interference with the metabolic processes. indirect effects on other nutrients, which might be rendered unavailable.

40. PARAMETERS WITH AGRONOMIC SIGNIFICANCE2. Toxic Ions Toxicity normally results in impaired growth, reduced yield, changes in the morphology of the plant, and even its death. The degree of damage depends on the: Crop, stage of growth, concentration of the toxic ion or ions relationships, climate, and soil conditions.

41. PARAMETERS WITH AGRONOMIC SIGNIFICANCE2. Toxic Ions The most common phytotoxic ions that may be present in municipal effluents in concentrations high enough to cause toxicity are Boron (B), Chloride (Cl), and Sodium (Na). Each can cause damage individually or in combination.

42. PARAMETERS WITH AGRONOMIC SIGNIFICANCE2. Toxic Ions Sodium and chloride are usually absorbed by the roots but can also enter directly into the plant through the leaves when moistened during sprinklerirrigation. This typically occurs during periods of high temperature and low humidity. Leaf absorption speeds up the rate of accumulation of a toxic ion and may be a primary source of toxicity.

43. PARAMETERS WITH AGRONOMIC SIGNIFICANCE2. Toxic Ions Boron can become toxic at levels only slightly greater than those required by plants for good growth. The predominant source of anthropogenic boron is domestic effluents, due to the use of perborate as a bleaching agent. As a result, boron can be found in urban wastewater at concentration levels as high as 5 mg/L (dry countries and concentrated sewage), with an average level around 1 mg/L

44. PARAMETERS WITH AGRONOMIC SIGNIFICANCE2. Toxic Ions It should be noted that boron at concentrations of less than 1 mg/L is essential for plant development, but higher levels can cause problems in sensitive plants. Most plants exhibit toxicity problems when the concentration of boron exceeds 2 mg/L.

45. PARAMETERS WITH AGRONOMIC SIGNIFICANCE3. Sodium Adsorption Ratio Sodium is a unique cation because of its effect on soil. When present in the soil in exchangeable form, sodium causes adverse physical-chemical changes, particularly to soil structure, which results in dispersion of particles and, consequently, reduced infiltration rates of water and air into the soil.

46. PARAMETERS WITH AGRONOMIC SIGNIFICANCE3. Sodium Adsorption Ratio As a rule, recycled water could be a source of excess Na in the soil compared to other cations (Ca, K, Mg), and for this reason it should be monitored. The most reliable index of the sodium hazard of irrigation water is the sodium adsorption ratio SAR. The sodium adsorption ratio is defined by Equation (2.1), where the ion concentrations are expressed in meq/L:

47. PARAMETERS WITH AGRONOMIC SIGNIFICANCE3. Sodium Adsorption Ratio If significant precipitation or dissolution of calcium due to the effect of carbon dioxide (CO2 ), bicarbonate (HCO3) and total salinity (ECw ) is suspected, an alternative procedure for calculating an adjusted sodium adsorption ratio (SARadj ) can be used. Where:

48. PARAMETERS WITH AGRONOMIC SIGNIFICANCE3. Sodium Adsorption Ratio Na = sodium in the irrigation water reported in meq/l Cax= a modified calcium value taken from Table 11, reported in meq/l. Cax represents Ca in the applied irrigation water but modified due to salinity of the applied water (ECw), its HCO3/Ca ratio (HCO3 and Ca in me/l) and the estimated partial pressure of CO2 in the surface few millimetres of soil (PCO2 = 0.0007 atmospheres) Mg =magnesium in the irrigation water reported in meq/l

49. PARAMETERS WITH AGRONOMIC SIGNIFICANCE3. Sodium Adsorption Ratio The threshold value of SAR of less than 3 indicates no restriction on the use of recycled water for irrigation, while severe damage could be observed when SAR is over 9, in particular for surface irrigation. At a given SAR, the infiltration rate increases as salinity increases or decreases when salinity decreases. Therefore, SAR and ECw should be used in combination to evaluate the potential problem. Recycled water is often high in sodium, and the resulting high SAR is a major concern in planning water reuse projects.

50. PARAMETERS WITH AGRONOMIC SIGNIFICANCE4. Trace Elements Urban wastewater may contain trace elements at concentrations that will give rise to high levels of such elements in the soil and cause undesirable accumulations in plant tissues and crop growth reduction. Trace elements are readily fixed and accumulate in soils with repeated irrigation with such recycledwaters and may render them nonproductive or the product unusable. Surveys of irrigation with recycled water have shown that more than 85% of the applied trace elements are likely to accumulate in the soil, most at or near the surface, and may be leached to groundwater.