Question

The composition of a municipal solid waste sample is given below:

Component	Percent by Mass	Moisture content (%)	Energy Content (kJ/kg. on as – discarded basis)
Food Waste	20	70	2500
Paper	10	4	10000
Cardboard	10	4	8000
Plastics	10	1	14000
Garden Trimmings	40	60	3500
Wood	5	20	14000
Tin Cans	5	2	100

The difference between the energy content of the waste sample calculated on dry basis and as discarded basis (in kJ/kg) would be ________

Answer 1

Component (1)	% By Mass (2)	Moisture content (%) (3)	dry content % (4) = 100 – (3)	Energy discarded (5) (kJ / kg)	Total dry mass (6) \(\frac{{\left( 2 \right) \times \left( 4 \right)}}{{100}}\)	Total energy as discarded \(\frac{{\left( 2 \right) \times \left( 5 \right)}}{{100}}\)
Food Waste	20	70	30	2500	6	500
Paper	10	4	96	10000	9.6	1000
Cardboard	10	4	96	8000	9.6	800
Plastics	10	1	99	14000	9.9	1400
Garden Trimmings	40	60	40	3500	16	1400
Wood	5	20	80	14000	4	700
Tin Cans	5	2	98	10	4.9	5
					= 60	= 5805 kJ/kg

Energy on dry basis: It will be the total energy when whole mass is dry.

In current situation only 60% mass is dry, so energy corresponding to 60% dry mass = 5805 kJ/kg

Using unitary method, energy corresponding to 100% dry mass \(= \frac{{5805}}{{60}} \times 100\) = 9675 kJ/kg

Energy based on as discarded basis = 5805 kJ/kg

So, difference = 9675 – 5805 = 3870 kJ/kg