Optimal conjunctive use model of treated wastewater and groundwater in Varamin irrigation network

In recent years, the use of treatment plants’ wastewater, as a component of
unconventional water has been considered as a supplementary to groundwater resources in
irrigation and drainage networks, while the rate of nitrogen leaching into the soil and
aquifer due to the use of chemical fertilizers and wastewater containing high nitrogen rates
should be assessed. In this research, development of cropping pattern optimization model
was addressed for quantitative-qualitative conjunctive use of unconventional surface water
(wastewater) and groundwater. Three objectives of the model were maximizing profits
from crop pattern, reducing nitrogen leaching and improving the rate of aquifer recharge.
The developed three-objective model was solved by three methods include Nonlinear
programming (NLP), particle swarm optimization (PSO) using weighted sum method and
multi-objective particle swarm optimization (MOPSO) algorithms for different scenarios in
Varamin irrigation network in 2012-2013 water year, and the results were compared. The
essential input data of two methods were collected by field tests and getting information
from different organizations. The results of solving the three-objective model by NLP
method indicated that the obtained profits from cropping pattern optimization, the water
use productivity and aquifer recharge were improved by 6, 22 and 29 percent, respectively
and on the other hand the conjunctive use of wastewater and groundwater and consumption
of nitrogen fertilizer were decreased by 13 and 85 percent, respectively. In PSO algorithm
using weighted sum method the obtained profits from cropping pattern optimization, the
water use productivity and aquifer recharge were improved by 7, 49 and 30 percent,
respectively and also the conjunctive use of wastewater and groundwater and consumption
of nitrogen fertilizer wre decreased by 35 and 88 percent, respectively. Finally in MOPSO
algorithm by forming Pareto front and then selecting the optimal solution by TOPSIS
method the obtained profits from cropping pattern optimization, the water use productivity
and aquifer recharge were improved by 7, 47 and 15 percent, respectively and the
objectives of conjunctive use of wastewater and groundwater and also consumption of
nitrogen fertilizer were decreased by 36 and 89 percent, respectively. The little difference
of about 0.002 to 0.01 between the results of objective functions in NLP and PSO for
different scenarios represents the high ability of PSO algorithm to find optimal solution.
Also the difference between the objective functions values of single-objective using
weighted sum method and multi-objective PSO algorithms is about 0.4 to 4 percent that
shows the proximity of PSO using weighted sum method and MOPSO algorithms results
in finding the optimal solution. Integrated quantitative-qualitative management of
irrigation water and wastewater resources in irrigation and drainage networks in terms of
controlling the environmental impacts of nitrogen leaching into the soil and groundwater
environment is an important issue, the proposed three-objective model of this paper can be
used to improve the performances of agriculture, environment and water resources sectors
in irrigation and drainage networks.

Optimal conjunctive use model of treated wastewater and groundwater in Varamin irrigation network Keywords:

Aquifer recharge , Multi-objective optimization , Nitrogen leaching , Particle Swarm Optimization (PSO) , Unconventional water