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Across 5. Species, family, or other larger group having no living members. 8. Sediment deposited during the treatment of sewage. 9. ............... fuels. 14. Not depleted when used. 15. Capable of decaying through the action of living organisms. 17. The surrounding or conditions in which a person, animal, or plant lives or operates. 19. A low area of land that is built up from deposits of solid refuse in layers covered by soil. 21. ....................... digestion uses bacteria and fungi to convert organic compounds to simple, inorganic forms. 22. The change of cider into vinegar. 25. .................. produced during anaerobic digestion. 26. Allows grit to settle. 30. A different or distinct form or version of something. 31. A nature reserve. 32. ............................. ensures that microbes can respire in aerobic condition to break down carbon compounds to carbon dioxide. 34. The total number of persons inhabiting a country, city, or any district or area. 38. Sewage or other liquid waste that is discharged into a body of water, etc. 39. A large area covered chiefly with tress and undergrowth. 41. Place that is natural for the life and growth of an organism. 42. A species limited to a few areas but in no immediate danger.

Down 1. Pathogen-free and drinkable water. 2. Used for refrigeration and in the manufacture of commercial chemicals and laboratory reagents. 3. Able to be maintained at a certain rate or level. 4. Pathogenic microbes which cause food poisoning. 5. A biological community of interacting organisms and their physical environment. 6. Use again or more than once. 7. A course metal grid used to remove floating debris such as sticks, paper, nappies and rags. 10. A species which is likely to become endangered if the causes of its decline continue. 11. The breakdown or decay of organic materials. 12. Seriously at risk of extinction. 13. Keeping some part of the environment unchanged. 15. The variety of plant and animal life in the world or in a particular habitat, a high level of which is usually considered to be important and desirable. 16. A furnace or apparatus for burning trash, garbage, etc., to ashes. 18. Energy derived from plant matter, that can be converted to fuel and is therefore regarded as a potential energy source. 20. The presence in or introduction into the environment of a substance which has harmful or poisonous effects. 23. .......... bank 24. Convert (waste) into reusable material. 27. Protect (environmental or cultural importance) from harm or destruction. 28. Visit to places having unspoiled natural resources, with minimal impact on the environment being a primary concern. 29. A relation between animals in which one organism captures and feeds on others. 31. .................................is the removal of faeces from waste water so that any pathogens they contain cannot infect drinking water. 33. The activity of searching for something. 35. Waterborne organisms causing dysentery. 36. The weather conditions prevailing in an area in general or over a long period. 37. Waste matter from domestic or industrial establishments that is carried away in sewers or drains for dumping or conversion into a form that is not toxic. 40. Untamed.