The company developing a state-of-the-art waste processing facility in Hampden says the project will probably be completed by the end of March — nearly a full year after the facility was supposed to begin receiving waste from more than 100 Maine towns and cities. Officials have attributed the delay to multiple factors, including weather that slowed construction last winter, a legal challenge to the project’s environmental permits and a changing market for recycled goods. With construction complete in March, the Fiberight plant should begin accepting waste in April, the company’s CEO, Craig Stuart-Paul, said during a tour of the three-acre construction site this week. But Stuart-Paul added that the timeline could stretch longer. “Things can go wrong,” Stuart-Paul said.