Editor Query Form Journal title: Encyclopedia of Environmental Management Author: Irene A. Tarimo Article id: E-EEM-120051985 The following queries have arisen during copy-editing your manuscript. Please provide an answer in the right-hand column below and on your proofs. Many thanks for your help.
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Query Please provide accessed date for Ref. [28].
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Municipal Wastewater Management: Use of Horizontal Subsurface Flow Constructed Wetland (HSSFCW) for Aquaculture and Agriculture Irene A. Tarimo and Tolly Mbwette Department of Environmental Studies, Open University of Tanzania, Dar es Salaam, Tanzania Abstract The research study was carried out in Moshi-Mabogini Tanzania to manage municipal wastewater using horizontal subsurface flow constructed wetland (HSSFCW) to obtain a standard outlet for reuse in aquaculture and agriculture. The aim of the study was to control environmental pollution and human toxicity emanating from heavy metals in order to reuse the safe resources. The grab wastewater samples were collected three times a week seasonally in one year from March 2010 to February, 2011. Fecal coliforms were measured in laboratories using standard methods of water and wastewater treatment (APHA, 2005). Heavy metals Cd, Cr, Cu, Pb, and Zn were analyzed in wastewater by an atomic adsorption spectrometry for evaluation of potential toxicological effects in fish. Temperature, DO, and pH were measured in situ using spectrophotometer (model 156, 2001). Heavy metals analyzed in wastewater were higher than the WHO (2006) and TBS (2005) standards as shown: the Cu mean concentration was 12.56 + 0.18 mg/L with a factor of six times more than permissible limits of 2.0 mg/L, while Pb 15.03 + 3.47 mg/L was 150 times more, and Cd 1.68 + 0.54 mg/L was about 16.8 times more than the standards of 0.1 mg/L for both Cd and Pb. The values of Zn and Cr were not significant (0.11 + 0.12 and 0.26 + 0.18 mg/L), respectively. Thus, it is dangerous to eat fish with high concentrations of Cd, Pb, and Cu found in water. The linear regression of Cu, Pb, and Cd showed a decreased trend of the concentration from the sampling points S1–S4 with (R 2 = 0.97, 0.93, and 0.91), respectively, showing significant levels in toxic heavy metals removal effectiveness by the HSSFCW. It is recommended to treat the wastewater more to remove the free heavy metals before going to the fish pond. More studies should focus on heavy metal concentrations in the sediments and the biotic components in the agricultural products to safeguard human health and other end users.
INTRODUCTION The entry discusses the effectiveness of horizontal subsurface flow constructed wetland (HSSFCW) in treating the municipal wastewater for reuse in aquaculture and agriculture. The rationale for municipal wastewater reuse worldwide emanates from the advancements in industrial developments, agriculture, and population growth that needs water to meet the high demand that surpasses the supply, which cause water stress. Thus, as water stress becomes an increasingly important concern in many places worldwide, more people are exploring the option of wastewater treatment and reuse in industry, aquaculture, and agriculture. Carelessness in implementing the technology for wastewater treatment and reuse may cause water-borne diseases and human toxicity from heavy metals. Hence, there is a need to prevent water-borne diseases, prevent offensive odors in the environment, remove toxic heavy metal solids/sludge, and convert into resources or fertilizers. This will safeguard both surface and ground waters from contamination and control environmental pollution. Individual homes, small communities, institutions, organizations, large towns, municipalities, and cities have used Encyclopedia of Environmental Management DOI: 10.1081/E-EEM-120051985 Copyright © 2014 by Taylor & Francis. All rights reserved.
various forms of wetland treatment: primary, secondary, tertiary, and higher treatment levels technology. Both HSSFCW and free water surface (FWS) wetlands have been implemented. HSSFCWs are designed to employ ecological processes found in natural wetland ecosystems. These systems utilize wetland plants, soils, and associated microorganisms to remove contaminants from wastewater. The treatment of wastewater using HSSFCWs technology provides an opportunity to create wetlands for environmental improvement, such as wildlife habitat, greenbelts, and other environmental amenities such as green playgrounds and landscaping. Tanzania benefits from the effective application of HSSFCW technology in water pollution control, wastewater management, sanitation, and water quality improvement to avoid environmental pollution. A review of the literature shows evidence of only very limited research and the use of HSSFCWs technology in the tropical regions. The goal of this entry was therefore to examine the recycling of wastewater in the ecosystems that it is safe so as to reduce water-related diseases in human beings and the risks associated with the toxic heavy metals. Moreover, it ensures the outlet from the HSSFCWs and the fish pond is safe before it is being reused in paddy irrigation to reduce poverty, child mortality, diseases, and environmental 1
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sustainability. Ultimately, this will help to meet the Millennium Development Goals by the year 2015 and the Tanzania National Strategy for Economic Growth and Reduction of Poverty (NSGRP II) by the year 2015, and the Development Vision by the year 2025. The specific objective was, therefore, to examine heavy metal pollution levels of cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn), and chromium (Cr) total and fecal coliforms in Mabogini-Moshi Municipality integrated wastewater treatment ecosystems and compare with WHO,[1–4] TBS,[5] and Tanzania Effluent Standards[6] acceptable values for the reuse of the treated municipal wastewater outlet in the environment for aquaculture and agriculture.
REVIEWED LITERATURE REVEALED TREATED MUNICIPAL WASTEWATER AS A RESOURCE HSSFCWs are a widely accepted technology for reducing wastewater BOD, TSS, and coliforms.[7–9] There has been an exponential growth in their application in the treatment of municipal wastewater.[8,10–17] For example, in the developing countries, wastewater treatment is not effective as the bulk of domestic and industrial wastewaters are still discharged untreated or preliminarily treated.[18] For instance, in Venezuela in South America, 97% of the sewage is discharged untreated into the environment,[19] while in Tanzania-Dar es Salaam 15% of domestic wastewater is discharged untreated into the Indian Ocean. The sub-urban areas of Dar es Salaam such as Msimbazi river and Kizinga river receive wastewater from industries like “Karibu Textile,” dye leachates, from agriculture, landfill dumping sites, untreated domestic wastewater, and ultimately discharge untreated wastewater into the Indian Ocean.[20] The discharge of untreated wastewater in the seas and oceans is part of the reasons why de-oxygenated dead zones are growing rapidly in the seas and oceans, which produce nuisance and odors around the environment. The climate change and ozone layer depletion caused by wastewaterrelated emissions of global warming gases like methane and nitrous oxide nitrogen compounds could rise by 50% by the year 2020.[21] The untreated wastewater can be treated to control environmental pollution, surface and ground water contamination through effective use of constructed wetland (CW) such as HSSFCWs and reuse the outlet in aquaculture and agriculture as well as landscaping. The importance of HSSFCW in treated municipal wastewater as a resource includes cost effectiveness with regards to construction, operation, maintenance, and reliability.[22] Provide ecological habitat for endangered species and migratory birds. Support a large population[23] as a resource and an essential part of modern ecology. Not only that, but also provide fishing sites, water supply, toxicant retention sites, and water for groundwater recharge. Wetlands also offer other mutual benefits in buffering storm waters and flood risks to humans and water bodies and they buffer
Municipal Wastewater Management
urban and countryside runoff with respect to the abatement of water and environmental pollution. HSSFCW can contribute to the reuse of treated wastewater as a resource in addressing poverty eradication by supporting aquaculture and agriculture.
EFFECTIVENESS OF HSSCW IN TREATING MUNICIPAL WW FOR REUSE IN AQUACULTURE This study ensures that the outlet from the HSSFCWs and the fish pond is safe before it is being reused in paddy irrigation to reduce poverty, child mortality, diseases, and environmental sustainability. It will help in meeting the Millennium Development Goals from http://www.un. org/millennium/numbers[1,4,6,7] directly and others indirectly as well as the Tanzania second National Strategy for Economic Growth and Reduction of Poverty (NSGRP II) by the year 2015 and the Development Vision by the year 2025. The sources of some toxic heavy metals and their effects in the body have been narrated by several literatures;[24–27] U.S. EPA, 2005a.[28–31] Cadmium (Cd) is naturally found in the rocks, coal, petroleum, industrial discharge, mining waste, metal plating, water pipes, nickel/ cadmium batteries, paints and pigments, plastic stabilizers, and landfill leachate. Cd can cause high blood pressure kidney and heart diseases. It destroys testicular cells in males and is toxic to aquatic biota. World Health Organization[3] and Tanzania Bureau of Standards (2004) permissible value of Cd in water and food is 0.1 mg/L. Copper (Cu) enters the environment from metal plating. Other sources are from agricultural, industrial, and domestic wastewaters, mining, and mineral leaching. Copper is an essential trace element but it is toxic to plants and algae at moderate levels. It causes stomach and intestinal distress, anemia, liver, and kidney damage in high doses, imparts adverse taste and significant staining to clothes and fixtures. The permissible value of Cu in water and food by the WHO[2] is 1.0 mg/L. Lead enters the environment from industry, mining, plumbing, gasoline, and coal and water additives in municipal water supplies. Lead is a highly toxic heavy metal that affects the chemistry of red blood cells in the body. It delays normal physical and mental development in babies and young children. It causes sight deficits in attention span, hearing, and learning in children. It increases blood pressure and cancer in adults. WHO[2] permissible value of Pb in water and food is 0.5 mg/L. Chromium enters the environment through natural and anthropogenic routes such as rocks, land erosion, plants, animals, air, water, soil, food, wood treated with copper dichromate, leather tanned with chromic sulfate and stainless-steel cookware. The major source of Cr III and VI are combustion of fossil fuels, domestic, and tanning/metallurgy/textile industrial wastes. Small amounts of chromium (III) are needed for human health. Chromium is widely used in manufacturing processes to make various metal alloys such as stainless
Municipal Wastewater Management
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steel. The effect of Cr VI is carcinogenic via inhalation and oral routes. Other effects include emission of toxic fumes flammable that may cause fires. In humans, it may cause lung and skin cancer, severe damage to the reproductive system and the unborn child, the gut, heart, liver, kidneys, and death. WHO[2] permissible value of Cr in water and food is 0.1 mg/L. Thus, the main objective is to examine the effectiveness of HSSFCW in the removal of toxic heavy metals from an integrated ecosystem for reuse in aquaculture and agriculture. Constructed wetland (CW) is defined as a wetland specifically constructed for the purpose of environmental pollution control and waste management, at a location other than existing natural wetlands.[32] There are two basic types of constructed wetland (CWs), the FWS wetland and the subsurface flow (SSF) wetland. Constructed surface flow (SF) and SSF wetlands include horizontal and vertical flow of water from inlet to the outlet. CWs mimic the optimal treatment conditions found in natural wetlands, but provide flexibility of being constructible at almost any location in the world and attract a wide variety of wildlife namely insects, mollusks, fish, amphibians, reptiles, birds, and mammals.[32] The plants can be classified as floating, submerged, or emergent depending on the dominating macrophytes in the wetland vegetation (Fig. 1). The SSF CW plants used in this study is the global Phragmites mauritianus. Emergent macrophyte systems may be subdivided into two categories based on the water flow pattern used.[3] The horizontal surface flow CW (HSFCW) or free water surface CW (FWSCW) systems are characterized by wastewater flow above and through the rooting medium in shallow basins. The reduced flow velocities provide ideal conditions for the removal of suspended solids and particulate organic matter while the biofilm or bacterial growth on the plant stems is responsible for organic and nitrogen degradation. The second category of emergent wetlands are the HSSFCW where wastewater is infiltrated into the porous medium with little or no water exposure on the surface. The infiltration can be at the inlet and wastewater flows horizontally under the bed and it is collected in the outlet at the end of the bed.[33] The infiltration can also be introduced vertically and the wastewater percolates down through different layers of the porous medium and the outlet is collected at the bottom.[34,35] In
Treatment wetlands
Surface flow (SF)
Floating plants
Submerged Emergent plants plants
DATA COLLECTION
Subsurface flow (SS)
Horizontal flow
Fig. 1 Treatment wetlands and plant types. Source: Modified from Kadlec & Wallace.[43]
both cases it is during the passage of wastewater through the rhizosphere that it gets cleaned by the microbiological degradation and the physicochemical processes.[24,25] HSSFCW have received popularity in Northern Europe and the United States.[13,26] The attraction of subsurface systems when compared to FWS and overland flow systems has been, in part, the perception of decreased risk of nuisance from flies, mosquitoes, odor, and greater efficiency in terms of land usage.[27] The outlet nitrate concentration is dependent on maintaining anoxic conditions within the wetland so that denitrification can occur. The SSF wetlands were superior to SF wetlands for nitrate removal. The 20 SF wetlands reviewed reported outlet nitrate levels below 5 mg/L; the 12 SSF wetlands reviewed reported outlet nitrate ranging from ,1 to ,10 mg/L.[25] Results obtained from the Niagara-on-the-Lake vertical flow systems show a significant reduction in both total nitrogen and ammonia ( .97%) when primary treated outlet was applied at a rate of 60 L/m²/day. The three types of CWs shown in Fig. 2 include: A) surface flow (SF); B) subsurface flow (SSF); and C) vertical flow (VF) patterns in which arrows show the flow direction. The type of CWs adopted in this municipal wastewater treatment is (B) HSSFCW. Municipal wastewater treatment through HSSFCW and reuse in agriculture and aquaculture for poverty alleviation is crucial in both developed and the developing countries.[29] HSSFCW are viable options to achieve advanced or secondary treatment of municipal wastewater.[30,31] Some advantages of HSSFCW in small communities, institutions, organizations, and rural areas are affordable, operatable, and reliable, have low construction, operation, and maintenance costs.[32,33] HSSFCW efficiency of removing pollutants from wastewater depends on factors such as: i) inlet wastewater quality; ii) climatic conditions of the area; iii) hydraulic loading time (HLT); iv) hydraulic retention time (HRT); and v) physical chemical characteristics of the system such as temperature, water depth, media selection, aspect ratio (length-to-width ratio of HSSFCW), dissolved oxygen (DO), and the hydrogen ion activity (pH).[34] HSSFCW polishes the wastewater treated by waste stabilization ponds (WSPs) or septic tanks to produce cleaned final outlet that can be reused in aquaculture and agriculture.[35,36]
Vertical flow
The data were collected from Mabogini-Moshi Municipality HSSFCW treating outlet from WSPs before reuse in aquaculture and agriculture that serves about 600,000 people. The area is located at the foot of Mount Kilimanjaro, the highest mountain in Africa, between latitude 3◦ 20′ and 3◦ 25′ south of the equator and 37◦ 20′ and 37◦ 25′ east of Greenwich meridian time. The climate of the area has monthly mean air temperatures between 22◦ C minimum and
4
Municipal Wastewater Management
Fig. 2 Three types of CWs, A, B, C. (Note that A is the surface flow, B the subsurface flow, and C the vertical flow constructed wetlands.) Source: Modified from Vymazal, Brix, et al.[44]
35◦ C maximum. The mean annual rainfall is about 1200 mm and the elevation altitude of 765 m above sea level. Grab wastewater samples were collected at the maturation pond two inlets (S1), outlet (S2)/inlet HSSFCW, outlet HSSFCW (S3)/inlet fish pond, and fish pond outlet (S4) weekly for a period of one year as shown in Fig. 3. DO, pH, and temperature were measured “in situ” with a Model (2001) HACH DR 2500 portable spectrophotometer fitted with different measuring probes. Heavy metals such as
cadmium, chromium total, copper, lead, and zinc were analyzed by flame atomic adsorption spectrometry (FAAS). The toxic heavy metals determined in the wastewater included chromium (Cr), copper (Cu), lead (Pb), and cadmium (Cd) as well as sulfides and phosphates. The wastewater was distilled and titrated to obtain the final readings. The associated compounds of sulfide and fecal coliforms were analyzed according to the standard methods for the examination of water and wastewater.[37]
Legend
Phragmites
WSP = Waste stabilization pond HSSFCW = Horizontal subsurface flow constructed wetland Inlet
To paddy farms Sampling point one (S1)
HSSFCW
Maturation WSP
Outlet Sampling point two
(S2) Sampling point three (S3)
Fig. 3 Cross-section sketch of the sampling sites (S1–S4). Source: This study.
Fish pond
Sampling point four (S4)
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RESULTS AND DISCUSSION
Legend
The summary of the results of the parameters analyzed in this entry is presented in Table 1. The table presents findings from the examined heavy metals removal efficiency from HSSFCW treating outlet from WSPs[38] for reuse in aquaculture and agriculture. To achieve this, the average concentrations must meet the required WHO (2) guidelines and the Tanzania Bureau of Standards.[5,6] The mean concentrations underlined in Table 1 seem to surpass the set standards. For instance, the mean concentration of copper (Cu) was 12.56 + 0.18 mg/L with a factor of six times more than permissible limits of 2.0 mg/L, while lead (Pb) (15.03 + 3.47 mg/L) is 150 times more and cadmium (Cd) (1.68 + 0.54 mg/L) is about 16.8 times more than the required standard concentration of 0.1 mg/L (1; 2; and TBS, 2004) for both Cd and Pb. Copper (Cu) is mostly associated with the sulfide fractions, while zinc (Zn) and lead (Pb) show affinity for oxides and sulfides. Byekwaso et al.[39] in Uganda and Ojo and Mashauri[40] reported that CWs were very efficient at retaining copper, nickel, cobalt, cadmium, iron, and nitrogen. They found the mean percentage removal of Cd, Cu, and Pb to be 20%, 33.3%, and 23%, respectively, which agrees well with this study that found removal of 24.8%, 25%, and 25% Cd, Cu, and Pb, respectively. A study by Mdamo[41] at Lake Victoria in Mwanza, Tanzania, reported the accumulation of lead at 0.38 mg Pb/g and zinc at 0.23 mg Zn/g in Kagondo Wetland plant rhizomes. Zinc concentration agreed well with this study, which falls below the WHO[2] and TBS[5] standards of 5.0 mg/L. Lead was below this study by a factor of 39.5 times more but above the standards of 0.1 mg/L. Vymazal and Krása[42] in Czech Republic reported the percentage removal of heavy metals efficiency was high for Cu and Zn, found to have been .82.3% and .97.5%, respectively, which are very close to this study. The low removal efficiency of heavy metals in this study may result from
Concentration (mg/L)
Cr Total
Zinc
Cu
Pb y=0 R² = #N/A
Cd
Sampling sites
Fig. 4 Average concentrations of the heavy metals along the sampling points of HSFCW.
Moshi-Mabogini CW being small in volume (583.5 m3) with a short retention time of 1 day for the work of treating about 3800 m3 outlet per day from Moshi Municipality. This suggests the construction of new big SSF CW downstream and to increase the retention time to up to 2–4 days in order to increase the wastewater treatment efficiency in the HSSFCW system. Fig. 4 gives the concentration trend of the heavy metals analyzed in the sampling sites. Linear regression of Cu, Pb, and Cd shows significant concentration decrease trend from S1 to S4 of the sampling points with (R 2 = 0.97, 0.93, and 0.91), respectively, which have very significant levels in toxic heavy metals removal effectiveness by the HSSFCW. R 2 values for Zn and Cr were not significant and are not shown. Figs. 5–7 give a separate concentration regression (R 2) trend of the three significant heavy metals analyzed. There is an increase in the linear regression of cadmium (Cd) treatment effectiveness from S1 inlet (maturation pond) through S4 outlet (fish pond). As in Cd, there is an increase in linear regression of copper (Cu) treatment effectiveness from S1 inlet, that
Table 1 Average concentration and standard deviation of the analyzed parameters Parameters
N
S1 inlet
Cd (mg=L)
48
4.201
Cr total (mg=L)
48
Cu (mg=L)
48
Pb (mg=L)
48
Zinc (mg=L)
48
Sulfide(mg=L)
48
FC (No.=100 ml)
48
pH
48
DO (mg=L)
48
Temp
( C)
48
S2 outlet
S3 outlet
S4 outlet
2.184
0.241
0.121
0.225
0.201
0.018
0.008
0.45
0.11
+0.12
+0.03
24.888
14.734
7.512
3.102
50.24
12.56
+9.51
+0.18
31.126
17.952
6.816
4.215
60.11
15.03
+12.27
+3.47
0.436
0.386
0.151
0.065
1.04
0.26
+0.18
+0.51
0.301 155
0.176
0.067
0.034
86.00
50.00
7.66
7.55
7.52
7.35
2.98
3.28
3.88
4.21
24.90
24.30
27.1
26
24.2
Total
Mean conc.
Std. dev.
Conf. 0.05(95%)
1.68
+1.92
+0.54
6.75
0.14
+0.12
+0.34
79.25
+56.19
+15.89
30.8
7.52
+0.13
+0.04
14.35
3.58
+0.56
+0.15
25.13
+1.35
+0.38
0.58 317
100.5
Note that the 48 values are of wastewater and the underlined mean concentration surpass the standards.
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Fig. 5 Average concentration of cadmium along HSFCW.
is the maturation pond through S4 outlet of the fish pond. Similar to Cd and Cu, there is an increase in correlation of lead (Pb) treatment effectiveness from S1 inlet of the maturation pond through S4 outlet of the fish pond. Cr total (0.11 mg/L) and Zn (0.26 mg/L) from the HSSFCW met the standards for outlet reuse in aquaculture and agriculture.
Municipal Wastewater Management
wastewater can be substantially removed by HSSFCW treating outlet from WSPs for reuse in aquaculture and agriculture. However, the effectiveness of this removal has been a bit lower than the standards. There are still some high concentrations of Cd, Cu, and Pb, which suggests that the reuse of the outlet in aquaculture and agriculture might not meet the required (WHO, 2008, TBS, 2011) standards for the heavy metal concentrations in fish. It is dangerous to eat fish because the toxic heavy metals of Cd and Pb in the HSSFCW outlet did not meet the permissible World Health Organization (WHO, 2008) and Tanzania Bureau of Standards (TBS, 2011) levels. However, the fecal coliforms removal met the standards of ,1000 CFU/100 ml of the outlet. Recommendations 1.
CONCLUSIONS AND RECOMMENDATIONS Conclusions This research shows that heavy metals Cd (R 2 = 0.905), Cu (R 2 = 0.969), and Pb (R 2 = 0.934) in Moshi Municipal
2.
3.
4.
Since lead (Pb = 15.03), cadmium (Cd = 1.68), and (Cu = 12.56) were found to be higher than the standards of Pb and Cd (0.1 mg/L) and Cu (2.0 mg/L), it is recommended to have more treatment of the wastewater to remove the heavy metals before going to the fish pond. This can be done by adding an extra HSSFCW downstream. The use of rechargeable light appliances is recommended instead of dry batteries that may contain cadmium, which add up in the ecosystem and stop using leaded gasoline. Biotechnology application by the use of a variety of agricultural and forestry by-products as biosorbent of toxic metals such as olive mill waste of Olea europea for Cr, Ni, Pb, Cd, Zn, and Cu is also important. More studies should focus on heavy metal concentrations in the sediments and the biotic components in the agricultural produce to safeguard human health and other end users.
ACKNOWLEDGMENTS
Fig. 6 Average concentration of lead along HSFCW.
The authors wish to thank the Government of Tanzania through the Open University for the financial support during the research period. Professor Sven Erik Jorgensen of the University of Copenhagen, Denmark, as the ecological modeling expert and an advisor is highly appreciated. Special thanks go to Moshi Urban Water and Sanitation Authorities (MUWSA) and the field work assistants as well as the laboratory analysis support from Ardhi University.
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Fig. 7 Average concentration of copper along HSFCW.
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