Microgrids are subsystems of the distribution grid which comprises small generation capacities, storage devices and controllable loads, which can operate either connected or isolated from the utility grid. A microgrid has the ability to increase energy efficiency and reduce emissions. This paper studies the microgrid environmental/economic problem, i.e. the problem of optimizing microgrid operations to fulfil a time-varying energy demand and operational constraints while achieving a tradeoff between microgrid running costs and emissions. The problem is posed as a multi-objective mixed-integer linear optimization problem, which is solved in an efficient way by using commercial solvers. A case study of a typical microgrid is investigated: simulation results show the feasibility and the effectiveness of the proposed approach.