Evaluating the Impact of Macroeconomic Policy Interventions and Recession on a Sewage Treatment PPP Project Using a System Dynamic Model

Table 1

Model variables.

No.	Name	Symbol	Unit	Function/value
1	Net present value	NPV	Dollars	∑(CI − CO)/(1 + i)^To
2	Cash inflow	CI	Dollars/year	Sewage treatment income + government subsidy
3	Cash outflow	CO	Dollars/year	Construction cost + operation cost + loan interest
4	Construction cost	Cc	Dollars/year	1.456 × 10^7
5	Operation cost	Co	Dollars/year	Operation cost = 0.29 million × (1 + annual growth rate)^time
6	Loan interest	Ci	Dollars/year	Loan fund × loan interest rate
7	Tax	Ct	Dollars/year	Sewage treatment income × tax rate
8	Minimum attractive rate of return	Rmin	%	8
9	Sewage treatment income	Is	Dollars/year	Concession price × actual quantity of sewage treatment
10	Concession price	P	Dollars/T	0.14
11	Actual quantity of sewage treatment		T/year
12	Influence coefficient of GDP growth rate on volume growth rate	μ	Dimensionless	1
13	Influence coefficient of GDP growth rate on volume volatility	σ	Dimensionless	0.8
14	Design volume of sewage treatment	Qd	T/day	1.15 × 10^4 T/Day
15	Minimum quantity of sewage treatment	Qmin	T/day	0.7 × design volume of sewage treatment
16	Initial quantity of sewage treatment	Qi	T/day	0.5 × design volume of sewage treatment
17	Adjusted volume	Qad	T/day	Min [max(Qac, Qmin), Qmax]
18	Government subsidy for this project	Gs	Dollars/year	Sewage treatment income-concession price × actual quantity of sewage treatment
19	Amount of loan	L		Construction investment × self-owned capital ratio
20	Loan interest	Li		Amount of loan × loan interest rate
21	GDP growth rate		%	6.5
22	Loan interest rate	Rl	%	7.5
23	Government investment ratio	Ri	%	0
24	Self-owned capital ratio	Rs	%	30
25	Value-added tax rate	Rt1	%	17
	Enterprise income tax rate	Rt2	%	25