Question

a) Your client is considering building a house in a rural area where a municipal sewage reticulation is not available (18 marks) i. Discuss with your client under what circumstances a septic tank should be used ii. iii. How does a drainage installation, including a septic tank, works What are the basic principles involved in its operation b) Identify the components of a solid concrete floor with a neat sketch-(4 marks) c) A contractor leaves mild steel reinforcement in the open air and it gets wet after heavy rainfall. Explain what is likely to happen to the reinforcement and what would be the consequence of this if it gets worst and the reinforcement is used in concrete. (3 marks)

Answer 1

(a.)

(i) Septic tank is the structure constructed within the premises of the bulding which is used for the decomposition of solid waste generated in that household. The decomposition is done through anaerobic process i.e in the absence of the air. Hence, the inconvenience caused is less/negligible when compared to areobic process.

A septic tank is used under following circumstances

• When there is no sewer pipes for the waste removal
• In water deficient areas where there is less water available for flow of sewage. The capacity of tank is 70liters per head.

(ii) The basic principles involved in its operation are

• The decomposition is done through anaerobic process
• The anaerobic bacteria acts on the waste produced and ddecomposes it in to smaller particles thus settling them at the bottom of the septic tank
• Any harmful gases produced during the process is let out through n air vent that is provided at a heigh
• If the rate of accumulation of sludge is more than the rate of decomposition periodical removal of waste should be done using a specially equipped truck.
• Usually septic tanks are cleaned once in 2-3 years

(iii) The human waste along with water from the water closet is reached to the septic tank by pipes. The modern septic tanks are having two horizontal chambers. The watste enters the first chamber where most of the decomposition is done the sludge is settled and the excess water is sent to the second chamber. When the second chamber is also filled the water free from sludge is drained to the drinage drirectly.