Domestic Wastewater Treatment and sustainable ...

EMPOWERS Regional Symposium: End-User Ownership and Involvement in IWRM Cairo, Egypt. November 13-17, 2005 __________________________________________________________________________________________________

Domestic Wastewater Treatment and sustainable Re-use. Closing the Loop Walid Abdel-Halim* and K.-H. Rosenwinkel Institute of Water Quality and Waste Management, Hannover University, Germany. * Originally from: Housing and Building National Research Centre, Cairo, Egypt. E-mail: [email protected]

Keywords: Sustainable treatment; Municipal Wastewater; UASB-pond; Water reuse; Developing Countries.

1. Introduction A supply of clean water is an essential requirement for the establishment and maintenance of diverse human activities. Water resources provide valuable food through aquatic life and irrigation for agriculture production. However, liquid and solid wastes produced by human settlements and industrial activities pollute most of the watercourses throughout the world. The increasing scarcity of water in the world along rapid population increase in urban areas gives reason for concern and the need for appropriate water management practices. Very little investment has been made in the past on sewage treatment facilities; water supply and treatment often received more priority than wastewater collection and treatment. However, due to the trends in urban development, wastewater treatment deserves greater emphasis. Currently there is a growing awareness of the impact of sewage contamination on rivers and lakes; therefore, wastewater treatment is now receiving greater attention from a lot of international organizations and government regulatory bodies. The greatest challenge in the water and sanitation sector over the next two decades will be the implementation of low cost sewage treatment that will at the same time permit selective reuse of treated effluents for agricultural and industrial purposes. Developers should base the selection of technology upon specific site conditions and financial resources of individual communities. Although site-specific properties must be taken into consideration, there are core parts of sustainable treatment that should be met in each case such as: No dilution of high strength wastes with clean water; Maximum of recovery and re-use of treated water and by-product obtained from the pollution substances (i.e. irrigation, fertilization); Application of efficient, robust and reliable treatment/conversion technologies, which are low cost (in construction, operation, and maintenance), which have a long lifetime and are plain in operation and maintenance; Applicable at any scale, very small and very big as well; Leading to a high self-sufficiency in all respects; Acceptable for the local population and comply with the regulations and standards.

2. Municipal wastewater treatment situation in developing countries In developing world, around 300 million urban residents have no access to sanitation and they are mainly low-income urban dwellers that are affected by lake of sanitation infrastructure.

__________________________________________________________________________________________________ Abdel-Halim, Walid. et al 1


Approximately two-thirds of the population in the developing world has no hygienic means of disposing excreta and an even greater number lack adequate means of disposing of total wastewater (Rose, 1999). Inadequate sanitation is one of the prime causes of disease. In the developing countries, the provision of sanitation is not keeping up with population growth. The total numbers of population with and without sanitation in all developing countries are shown in (figure 1) (WHO, 1997b). 3.5 3

1000 million

In Egypt as an example for developing MENA countries, more than 95% of the Egyptian villages are not provided with wastewater collection and treatment facilities. There are about 4000 Egyptian rural-areas with a population ranging from 1000 to 20000 capita. The wastewater produced from houses in these rural areas is mainly treated in septic tanks. Communities without municipal water range between 23 and 36 percent.

2.5 2 1.5 1 0.5 0 1990

1994

2000

Year

With Sanitation

Without Sanitation

Figure 1: Population with and without sanitation, all developing countries. Source (WHO, 1997b)

As concerns the lack of sanitation, the coverage is between 6 and 17 percent. The former communities rely on unimproved water supplies (e.g., wells, rivers, ponds, canals and unprotected springs) and the latter on unimproved sanitation facilities as holes in the ground, bushes and other places where human waste is not contained to prevent it from contaminating the environment. Communities with improved water and sanitation do not all have the same services. It should be noted that the functioning or the improvements in sanitation facilities also depends on its connection to a sewer system. However, only some of the urban households have access to sewer systems. To meet the demands for water and wastewater services in the next decade, Egypt as one of the MENA developing countries will have to invest 5-7 billion US$, which is well above the available national resources (USAID, 2002). Providing rural areas in Egypt with water supply (more than 98% of rural areas in Egypt have water supply) has resulted in an increase of wastewater production, which increases the urgent need for proper facilities for wastewater collection and treatment. The treatment systems in developing countries are not successful and therefore unsustainable because they were simply copied from Western treatment systems without considering the appropriateness of the technology for the culture, land, and climate. Often local engineers educated in the Western development programs supported the choice for the inappropriate



systems. Many of the implemented installations were abandoned due to the high cost of running the system and repairs (van Leir, 1998). In the growing number of conflicts between agricultural and domestic use of scarce water resources, an increased use of treated wastewater for irrigation purposes is vital. Wastewater is composed of over 99% water. In a developing urban society, the wastewater generation is usually approximately 30-70 m3 per person per year. In a city of one million people, the wastewater generated would be sufficient to irrigate approximately 1500-3500 hectare (SIDA, 2000). Innovative and appropriate technologies can contribute to urban wastewater treatment and reuse. The benefits of reusing treated (waste) waters must also be measured against the cost of not doing so at both the economic and environmental level. The costs of implementing zerodischarge organic waste to agriculture recycling schemes may not be expensive. Full-scale implementation of urban organic waste to agriculture systems could cost as little as 5-6 USD million for a city of 1 million people (Rose, 1999). Based on the presented situation, it becomes important to investigate and improve further the functioning and performance of wastewater treatment technologies currently in use specially in developing region. The present trend is to use conventional systems in large-sized cities, while for medium and small-sized towns non-conventional technologies are usually considered. The systems commonly implemented in the latter years are waste stabilization ponds and a variety of anaerobic reactors (i.e. septic and imhoff tanks, anaerobic filters, UASB reactors, and anaerobic digesters). Combinations of all these systems are also currently in use in various countries in an effort to find cost-effective alternatives for pollution control. Nevertheless, it is necessary to carry out more investigations on these wastewater treatment technologies, so that they not only remove both organic matter and pathogens in the most efficient way possible but taking into consideration the critical factors that hinder their sustainability in developing countries. Such improved technological alternatives must be suitable to the diverse political, economical, technical and social contexts of the different countries.

3. Sustainable technologies for wastewater treatment In order to achieve ecological wastewater treatment, a closed-loop treatment system is recommended. Many present day systems are a “disposal-based linear system”. The traditional linear treatment systems must be transformed into the cyclical treatment to promote the conservation of water and nutrient resources. Using organic waste nutrient cycles, from point-ofgeneration to point-of-production, closes the resource loop and provides an approach for the management of valuable wastewater resources. Failing to recover organic wastewater from urban areas means a huge loss of life-supporting resources that instead of being used in agricultural for food production, Fill Rivers with polluted water. The development of ecological wastewater management strategies will contribute to the reduction of pathogens in surface and groundwater to improve public health. “The goal of ecological engineering is to attain high



environmental quality, high yields in food and fiber, low consumption, good quality, high efficiency production and full utilization of wastes”(Rose, 1999). There is currently a wide variety of systems, which can be successfully applied for wastewater treatment. They should however be selected on the basis of the specific local context. Generally, in industrialized countries the number of suitable alternatives may be more limited due to stricter regulations. In developing countries, however, the number of choices may be higher as a result of the more diverse discharge standards encountered. In this sense, effluent standards vary from the very conservative to the very relaxed. Likewise, the cost component and the operational requirements, while important in industrialized countries, play a much more decisive role in industrializing countries. Also the high contrast between urban and rural areas is an important feature. The selection of wastewater treatment systems must based on important aspects such as efficiency, reliability, sludge disposal…etc. A comparison of the most important aspects in the selection of wastewater treatment systems had analysed in the context of both developed and developing countries (table 1). It shows that in developed countries the critical items are: efficiency, reliability, sludge disposal and land requirements, whereas in developing countries the critical items are construction costs, sustainability, simplicity and operation costs. These factors, although important in developed countries cannot be considered critical. Therefore, each situation must be analysed individually and local conditions must be incorporated from the very beginning of the project cycle. Table 1: Important factors in the selection of wastewater treatment system in developed and developing countries (von Sperling, 1995). Factor

Developed countries Critical

Important

Developing countries Critical

Important

Efficiency

x

x

Relaibility

x

x

Sludge disposal

x

x

Land requirements

x

x

Environmental impacts

x

x

Operational costs

x

x

Construction costs

x

x

Sustainability

x

x

Simplicity

x

x

The consideration of multiple alternatives is the best way to reach an efficient, economical and adequate solution not only at the design stage, but also throughout the operational life of the wastewater treatment plant.



4. Demonstration of Anaerobic technology for wastewater pre-treatment Answering to the high priority request concerning the sustainability criteria of the wastewater treatment technology, the anaerobic wastewater treatment should be regarded as the core method of a sustainable wastewater management strategy due to its benefits and enormous potentials such as: Little (if any) use of mineral resources and energy; Enabling production of resources/ energy from wastes; Pairing high efficiency with long term of lives; Applicable at any place and at any scale; Plain in construction, operation and maintenance. Moreover, although conventional aerobic treatment systems generally provide excellent treatment efficiency, they do not fully meet the criteria needed for a sustainable wastewater management strategy (Lettinga, 1995, 2001). 4.1. Application of anaerobic technology Nowadays, the anaerobic technology has a very wide application in the field of anaerobic digestion whether for liquid or bio-solid waste. Figure 2 shows the main overall application of the anaerobic digestion.

Anaerobic Digestion

Liquid wastes: - Municipal wastewater - Industrial wastewater

Biosolid wastes: - Wastewater sludges - bio-solid waste - Agriculture wastes

Figure 2: Main overall application of the anaerobic digestion

4.2.

Benefits and drawbacks of anaerobic municipal wastewater treatment

Based on the past experiences and learned lessons in the municipal wastewater treatment, the anaerobic technology proved a very good performance and efficiencies due to its positive advantages against aerobic ones. The main advantages and drawbacks of the anaerobic municipal wastewater treatment systems are shown in table 2.

Table 2: Advantages and drawbacks of anaerobic municipal wastewater treatment systems. (Lettinga, 2001; Foresti, 2001; Zeeman and Lettinga 1999; Jim Field, 2002).

Advantages Drawbacks 1. Economy of the process, a substantial 1. Need for post treatment, in some cases saving in operational costs as no energy to comply with the effluent standards, a is required for aeration as well as low



investment costs of construction and maintenance.

simple/poor post treatment is necessary.

2. Little available experiences, sometimes especially with the full-scale application Positive instead of negative energy balance, on the contrary energy is at low and or moderate temperatures. produced in the form of methane gas, 3. Solubility of biogas, significant amount which can be utilized for heating and of produced biogas dissolved in water electricity production. i.e. instead of and remains in the effluent especially using 1 KWh of electricity, 1 KWh can for low strength wastewater. be produced instead in form of methane. 4. Non utilized methane, produced 3. High performance, the process can methane during anaerobic municipal handle high hydraulic and organic wastewater treatment is often not loading rates. Thus, the applied utilized for energy generation. technologies are rather compact and reduce the volume of post treatment stages. 2.

4. Simplicity, the technologies are simple in construction, operation, monitoring, and maintenance, consequently they are cost-effective technologies. 5. Flexibility and sustainability, the systems can be applied everywhere and at any scale and working with high treatment efficiencies. 6. Low generation of surplus sludge, the excess sludge production is very low. Additionally, the sludge is well stabilized and easily dewatered due to high solids retention time. Hence, lower secondary costs for sludge handling (dewatering, transport and disposal/reuse). 7. Possibility of nutrients recovery, the valuable nutrients (N, P and K) is conserved which give high potential for crop irrigation and aquaculture when reusing the anaerobically treated wastewater in agriculture purposes.



8. Feasibility, the anaerobic technology is feasible for a wide range of waste and wastewaters whether complex in composition, very low or very high strength as well as at low and high temperatures. 4.3.

Simplified concept of anaerobic wastewater treatment and re-use

4.3.1. Natural anaerobic UASB-pond The hereafter Concept (figure 3) offers environmentally sound and economical attractive solutions for wastewater treatment and re-use in developing countries. The wastewater is anaerobically treated using a natural UASB-Pond (figure 4) to win all of the anaerobic treatment benefits as winning of biogas as an alternative source of energy as well as less quantity of sludge with a very good stabilization status, and cost effective benefits as low capital, operation and maintenance cost. The treated wastewater will be naturally disinfected in polishing pond and re-used for agriculture purposes to recover the high valuable nutrients N, P and K. The main aim of the Concept is the treatment of municipal wastewater and sustainable re-use for natural eco-systems maintaining by the development of a low cost technology in developing countries. The next illustrated below diagram figure 9 describes the main Concept that the clean water is entering to the 1 Biogas Energy city for the domestic use only but the agriculture Domestic use Wastewater 2 Soil Fertilizer Clean Water Anaerobic treatment City Demand use will be by using of the Agriculture use treated wastewater 3 Saving for clean Post treatment produced from this water Concept. Alternative source of energy

Improvement of soil characteristic and productivity

NO

Direct Irrigation Water

Restricted Irrigation

Soil Reclamation

Ground Water Recharching

Also Concept produces not only a water resource for irrigation but also Figure 3: Integrated Concept for Wastewater produces an alternative Treatment and Re-use sources of energy in form of biogas to be converted to heat or electricity to save the usual energy resources, also it produces a good stabilized sludge which can be used as a fertilizer to enrich and improve the soil characteristics. The treated wastewater will be used as a source of nutrients for soil, i.e. recovery of these nutrients will be done to use them in soil reclamation. Improvement of soil productivity Indirect irrigation Water

Performance of UASB-Pond reactor. The results from the used UASB pond in the tropical conditions a reduction in BOD up to (80-90) %. The UASB pond technology is feasible in an urban developing world context because of its high organic removal efficiency, simplicity, lowcost, low capital and maintenance costs. Typically UASB ponds have low sludge production



(0.02-0.2 kg/kg COD removed) and low energy needs. The biogas yield will be about 60-75 % CH4 and 20-30% CO2, and then it will be a good, feasible renewable energy source to be used at a low cost concept. Construction, O&M, and monitoring costs of treatment and disposal with this Concept= (143-218) €/m3 or (29-44) €/P.E.

Without UASB-Pond

With UASB-Pond

Figure 4: Natural UASB-pond reactor

4.3.2. Components of large anaerobic treatment plant in Developing countries Because of the limited financial resources, there is a definite need for a cost-effective appropriate technology for sewage treatment system. The UASB reactor technology may be mostly attractive option for sewage treatment for developing countries, because it can be used at small or large scale, in technically simple, lower cost. In developing countries such as India and Colombia the UASB was executed in full scale to treat the municipal wastewater. Each anaerobic treatment plant consists of the following main elements, illustrated in Figure 5: • overflow bypass and flow measurement structures • preliminary treatment structure • coarse and fine screens gas holder

raw wastewater grit trap

excess flared

splitter box

screens

to grit disposal

UASB reactor

UASB reactor

sludge drying beds

facultative lagoon

sludge to agriculture effluent to reuse or disposal

Figure 5: Flow Diagram of a UASB Treatment Plant



• • • •

grit trap enhanced primary treatment structures (UASB reactor modules) by-product handling structures (biogas handling and using; sludge handling) post-treatment structures (simple, low cost technique)

Table 3 gives the average removal efficiencies the UASB anaerobic treatment for oxygen consuming substances (BOD5 and COD) and total solids for the four treatment plants visited, including three treating municipal wastewater at Bucaramanga, Colombia; Mirzapur and Kanpur in India and one treating a mixture of tannery and municipal wastewater effluents, also in Kanpur.

Table 3: Comparison of average influent and reactor effluent quality and removal of four full scale UASB reactors Municipal Wastewater Parameter

Mixed wastewater

Bucaramanga, Colombia

Mirzapur, India

Kanpur, India

Kanpur Indea

Design peak capacity (MLD)

42

14

5

36

Operating capacity (MLD)

36

10

4.8

21.8 1183

Average organic loading COD

(mg/l)

400

360

560

BOD5 TSS

(mg/l) (mg/l)

150

180

210

484

230

360

420

1000 57

Average removal efficiency COD

(%)

65

61

74

BOD5 TSS

(%) (%)

75

66

75

63

70

70

75

56

Average HRT Influent teperature range Gas production

4.4.

(h)

5

8

6

5.2

(°C)

23-25

21-30

20-30

22-30

(m 3/d)

3300

500

480

─

Options for post treatment of anaerobically treated wastewater for re-use in irrigation purposes.

Although anaerobic reactors are effective at stabilizing organic material by degrading carbonaceous oxygen demand to methane and carbon dioxide, a typical anaerobic enhanced primary effluent has substantial residual oxygen demand, mostly from the reduced form of nitrogen, ammonia. The readily oxidizable residual oxygen demand may be dealt with in an additional aerobic treatment step or conversion to plant biomass in an integrated treatment and production system. To re-use the treated wastewater in irrigation purposes, the effluent quality must comply with the WHO guidelines for use of wastewater in agriculture and aquaculture, which were adopted in 1989 as a result of the consensus of a group of experts that met in 1985 in Engelberg, Switzerland. The group examined the risks of wastewater reuse and ranked the relative risks of infection from microbes and parasites as follows: 1. High with intestinal nematodes; 2. Moderate with bacterial infections and diarrheas;



3. Minimal with viral infections and diarrheas and hepatitis A; and 4. High to nonexistant with trematode and cestode infections, schistosomiasis, clonorchiasis and taeniasis, depending on local practices and circumstances. Table 4: Recommended Microbiological Quality Guidelines for Wastewater Use in Agriculture

Category

Reuse Conditions

A

Irrigation of crops likely to be eaten uncooked; sports fields, public parks

B

C

Irrigation of cereal, industrial and fodder crops, pasture and trees

Localized irrigation category B crops if worker and public exposure does not occur

Intestinal Nematodes (arithmetic mean of no. eggs/liter)

Fecal coliforms (geometric mean of no. per 100 ml)

workers, consumers

≤1

≤ 1,000

workers

≤1

No standard recommended

None

N/A

N/A

Group Exposed

Wastewater treatment expected to achieve required microbiological quality

Series of stabilization ponds designed to achieve the microbiological quality indicated, or equivalent treatment

Retention in stabilization ponds for 8-10 days for equivalent helminth and fecal coliform removal

Pretreatment as required by irrigation technology, but not less than primary sedimentation

Aerobic treatment of an anaerobically treated enhance primary effluent stabilizes the residual oxygen demand in the highly reduced effluent and can be designed to remove significant amounts of nutrients. A normally functioning UASB reactor can remove an average of 65 percent of COD (range: 50-75 percent), 80 percent of BOD5 (range 70-90 percent) and 75 percent of suspended solids (range 60-85 percent). Beginning with a typical municipal raw wastewater, this level of treatment will generally result in a treated effluent that corresponds to an “enhanced primary” quality, intermediate between primary and secondary (between 30-70 mg/l for BOD5) (Alaerts et al., 1990). An effluent less than secondary quality will generally not meet environmentally sound effluent discharge standards and will definitely need further treatment to be safe for reuse in agriculture. The post-treatment should be designed to improve the effluent quality in the following parameters (APHA et al, 1981): •

pathogen contamination (measured by the index of E. coli);

•

residual organic material (COD/BOD5);

•

oxygen demand from the reduced forms of N and S;

•

residual suspended solids (TSS)

•

inorganic N and P (nutrients)

The treatment systems, which could be used for post treatment, can be summarized as follows:



1. Activated Sludge; 2. Aerated bio filters; 3. Expanded granular sludge bed reactor; 3. Rotating biological contactor (RBC); 4. Dissolved Air Flotation (DAF); 5. Chemical post treatment; 6. Trickling Filters; 7. Waste stabilization ponds; 8. Polishing ponds; 9. Constructed wetlands; 10. Aquating farming systems; 11. Land treatment 5. References 1.

John Todd and Beth Josephson (1996): 12 Principals for designing natural wastewater treatment, Ecological Engineering 6, pp. 109-136.

2.

G. Lettinga, J.B. van Lier, J. van Buuren, G. Zeeman.(2001): Water Science and Technology 43(6), 181-188.

3.

Johan Verink (2000): Pond type UASB-Reactor for wastewater treatment, and patented works for three phase separator (PCT/DE 01/02298).

4.

USAID, http://www.usaid.gov/regions/ane/newpages/perspectives/egypt/egwater.htm

5.

Rose, G.D. (1999). Community-based technologies for domestic wastewater treatment and reuse: options for urban agriculture, N.C. Division of Pollution Prevention and Environmental Assistance, CFP Report Series: Repot 27, 1999.

6.

WHO (1997b). Health and environment in sustainable development, five years after the Earth Summit. WHO. Geneva, Switzerland.

7.

WHO-UNICEF (2000). Global Water Supply and Sanitation Assessment Report, WHO and UNICEF Joint Monitoring Programme for water supply and sanitation (JMP).

8.

SIDA (2000). Water and Wastewater Management in Large to Medium-sized Urban Centers

9.

Lier J. van, Pol, Seeman, Lettinga (1998). Decentralized urban sanitation concepts: prespectives for reduced water consumption and wastewater reclamation for reuse., EP& RC Foundation, Wageningen, Netherlands, Sub-Department of Environmental Technology, Agricultural University.

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