How to use the angularfire2/firestore.AngularFirestoreModule.enablePersistence function in angularfire2

VoteComponent,
		VoteDecisionComponent,
		DelegateDialogComponent,
		NavmenuComponent,
		ForumComponent,
		VoteNamePipe
	],
	imports: [
		// Angular //
		BrowserModule,
		BrowserAnimationsModule,
		FlexLayoutModule,
		FormsModule,
		// Firebase //
		AngularFireModule.initializeApp(environment.firebaseConfig),
		AngularFirestoreModule.enablePersistence(),
		AngularFirestoreModule,
		CoreModule,
		// Material //
		MatButtonModule,
		MatCheckboxModule,
		MatToolbarModule,
		MatIconModule,
		MatButtonToggleModule,
		AppRoutingModule,
		MatTabsModule,
		MatListModule,
		MatFormFieldModule,
		MatSelectModule,
		MatInputModule,
		MatDatepickerModule,
		MatNativeDateModule,

import { SharedModule } from '../shared/shared.module';

import { NoteService } from './note.service';

import { NotesListComponent } from './notes-list/notes-list.component';
import { NoteDetailComponent } from './note-detail/note-detail.component';

import { AngularFirestoreModule } from 'angularfire2/firestore';

@NgModule({
  imports: [
    CommonModule,
    FormsModule,
    SharedModule,
    AngularFirestoreModule.enablePersistence(),
  ],
  declarations: [
    NotesListComponent,
    NoteDetailComponent,
  ],
  providers: [NoteService],
})
export class NotesModule { }

];

@NgModule({
  declarations: [
    MessagesComponent
  ],
  imports: [
    CommonModule,
    FormsModule,
    RouterModule.forChild(routes),

    FlexLayoutModule,
    MaterialModule,
    AngularFireModule.initializeApp(environment.firebase),
    AngularFireDatabaseModule,
    AngularFirestoreModule.enablePersistence(),
    AngularFireAuthModule,
    AngularFireStorageModule
  ],
  providers: [
    RtdbService, FirestoreService
  ]
})

export class MessagesModule {
}

export {RtdbService, FirestoreService};

//environments
import { environment } from '../environments/environment';

//routes
import { appRoutes } from './routes';

@NgModule({
  declarations: [
    AppComponent,
    LoginpageComponent,
    DashboardComponent
  ],
  imports: [
    BrowserModule,
    AngularFireModule.initializeApp(environment.config),
    AngularFirestoreModule.enablePersistence(),
    FormsModule,
    HttpModule,
    RouterModule.forRoot(appRoutes)
  ],
  providers: [
    AuthguardService,
    AuthService,
    AngularFireAuth,
    XltofirestoreService
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }