94
T. Gichamo et al.
where Q(A
) has the second minimum values of Q i and D Q = 1/(m − 1) where
m denotes the number of the alternatives then A
Condition 2: (Acceptable stability)
A
must have the best value/s of the R i and/or S i amongst the other alternatives.
In this method, if one of the conditions is not satisfied, then the compromise
solutions set can be proposed as below:
• If only the second condition is not satisfied; A
and A
• If the first condition is not satisfied; A
, A
, . . . A
M where M determined as the
maximum decision points satisfy the condition Q(A
M
) − Q(A
) < D Q.
For the ranking of best wastewater treatment alternative, three most familiar steps
should be considered are the required sewage quality, factors affecting management
and applications namely: environmental, economic, and land availability (Tsagarakis
et al. 2001; Sperling and Chernicharo 2005). The appropriateness of natural wastewater treatment alternatives could mainly be ranked by the effectiveness of system efficiency, minimum specific footprint to minimize land requirements, minimum energy
utilization, costs (operation and maintenance), and little or no subjectivity to seasonal
or climate changes (Qian et al. 2007; Srdjevic et al. 2017). Moreover, different studies
compared various natural wastewater treatment methods through different models
have mainly focused on the above mentioned or closely related criteria. For instance,
Ouyang et al. (2015) evaluated slow rate land treatment, rapid infiltration land treatment, overland flow treatment, stabilization pond and constructed wetland using the
above mention comparison criteria and Zeng et al. (2007) compared triple oxidation
ditch, sequencing batch reactor and anaerobic single oxidation ditch by hierarchy
gray relation method using land size, removal of phosphorous and nitrogen pollutants, plant stability and sludge disposing effects. In the current study, five natural
wastewater treatment techniques such as waste stabilization pond (SP), constructed
wetland (CW), use of aquatic plants (AP), soil filter (SF) and reuse of wastewater for
irrigation (RWI) using land requirements (LR), capital cost (CC), pollutants removal
efficiency (PRE), maintenance cost (MC), hydrogeological risks (HGR) and health
risk as comparison criteria. The criteria in this study were mainly selected to focus on
the environment, health, and economic issues. Economic factors are valuated based
on maintenance, operation, and treatment costs, also land is evaluated by economic
terms and costs in natural wastewater treatment methods is very cheap because most
of the system components are operated without external source energy (Crites et al.
2006; Kivaisi 2001). Health-related issues are the basic health problems for the people
living around wastewater treatment areas or peoples working onsite which originated
from wastewater such as heavy metals, toxins, and other pathogens. The environmental factors focus on the potential impacts of the processes on hydrology, lithology,
and ecology. Natural wastewater treatment methods are usually carbon-free and it
is a smart-wastewater treatment method. For the wastewater treatment method to be
classified as the best, it must be low cost, carbon emission-free/minimum carbon
emission, and guarantee environmental safety and sustainability.
T. Gichamo et al.
where Q(A
) has the second minimum values of Q i and D Q = 1/(m − 1) where
m denotes the number of the alternatives then A
Condition 2: (Acceptable stability)
A
must have the best value/s of the R i and/or S i amongst the other alternatives.
In this method, if one of the conditions is not satisfied, then the compromise
solutions set can be proposed as below:
• If only the second condition is not satisfied; A
and A
• If the first condition is not satisfied; A
, A
, . . . A
M where M determined as the
maximum decision points satisfy the condition Q(A
M
) − Q(A
) < D Q.
For the ranking of best wastewater treatment alternative, three most familiar steps
should be considered are the required sewage quality, factors affecting management
and applications namely: environmental, economic, and land availability (Tsagarakis
et al. 2001; Sperling and Chernicharo 2005). The appropriateness of natural wastewater treatment alternatives could mainly be ranked by the effectiveness of system efficiency, minimum specific footprint to minimize land requirements, minimum energy
utilization, costs (operation and maintenance), and little or no subjectivity to seasonal
or climate changes (Qian et al. 2007; Srdjevic et al. 2017). Moreover, different studies
compared various natural wastewater treatment methods through different models
have mainly focused on the above mentioned or closely related criteria. For instance,
Ouyang et al. (2015) evaluated slow rate land treatment, rapid infiltration land treatment, overland flow treatment, stabilization pond and constructed wetland using the
above mention comparison criteria and Zeng et al. (2007) compared triple oxidation
ditch, sequencing batch reactor and anaerobic single oxidation ditch by hierarchy
gray relation method using land size, removal of phosphorous and nitrogen pollutants, plant stability and sludge disposing effects. In the current study, five natural
wastewater treatment techniques such as waste stabilization pond (SP), constructed
wetland (CW), use of aquatic plants (AP), soil filter (SF) and reuse of wastewater for
irrigation (RWI) using land requirements (LR), capital cost (CC), pollutants removal
efficiency (PRE), maintenance cost (MC), hydrogeological risks (HGR) and health
risk as comparison criteria. The criteria in this study were mainly selected to focus on
the environment, health, and economic issues. Economic factors are valuated based
on maintenance, operation, and treatment costs, also land is evaluated by economic
terms and costs in natural wastewater treatment methods is very cheap because most
of the system components are operated without external source energy (Crites et al.
2006; Kivaisi 2001). Health-related issues are the basic health problems for the people
living around wastewater treatment areas or peoples working onsite which originated
from wastewater such as heavy metals, toxins, and other pathogens. The environmental factors focus on the potential impacts of the processes on hydrology, lithology,
and ecology. Natural wastewater treatment methods are usually carbon-free and it
is a smart-wastewater treatment method. For the wastewater treatment method to be
classified as the best, it must be low cost, carbon emission-free/minimum carbon
emission, and guarantee environmental safety and sustainability.