Sampling points should be a true representative of the given occupation sub-group. In a residential area, the sampling point should represent waste coming from at least 100 families.

If an average value of refuse characteristics for the full city is to be given, weightage factors are calculated. The weightage factor for a specific occupation category will be the ratio of the weight of refuse produced from that occupation group divided by the total weight produced from the city. The average values of characteristics from different occupation sub-groups are then multiplied by the weightage factor to compute the average value for the city.

1. Sample Size

In studies carried out, it was found that a 100 kg sample gave as much accuracy as a 1000 kg sample. When the collection at a point is small and a 100 kg sample cannot be obtained, smaller samples could be used for analysis. Repetitive sampling and analysis would provide a more representative data. At least ten grab samples should be taken from a number of points in the refuse mass both horizontally as well as vertically and then mixed to get the composite sample.

2. Number of Samples

Carruth and Klee have given the following method for determining the number of samples:

$$n = \left( \frac{Z.S}{d} \right)^2$$

Where -

n = number of samples required

Z = standard normal deviate for the confidence level desired

S = estimated standard deviation (transformed basis)

d = sensitivity (transformed basis)

At 90% confidence, Z = 1.645, S = 0.1413. The sensitivity transformed basis is determined as follows: transform x and either $x + \Delta$ or $x - \Delta$ by the arcsin transformation, where x is the expected percentage of the component in question and $\Delta$ is the desired precision for the percentage to be estimated.

3. Physical Analysis

The sample so collected should be sorted out physically into various ingredients such as paper, glass, plastics, etc. on a sorting platform. The individual components are separated, stored in bins and weighed. The weights are then expressed as a percent of the original sample.

The density of the material is measured. The physical analysis is on a wet weight basis which helps in choosing the system for collection and processing. A large organic content indicates the necessity for frequent collection and removal. The larger amount of paper indicates that waste can be thermally treated. Plastics in high concentration indicate possible problems in their disposal. A large percentage of ash indicates that putrefaction will not readily occur and that collection frequency could be less. In such a case, sanitary landfilling would be a better method.

4. Chemical Analysis

From the mass used for physical analysis a 500 gms sample is taken for moisture determination and heated overnight at $100^0C$ to obtain weight loss. This loss is expressed as a percentage of total weight. Normally moisture content is determined as soon as the sample is collected which helps in the choice of processing and disposal methods.

The total of 100 kg sample used for physical analysis is now reduced to 12.5 kg by using the method of quartering in which the mass is divided into 4 parts and 2 diagonally opposite parts are taken and mixed while the other 2 are discarded.

The 12.5 kg sample is then dried, ground in a hammermill or a grinder till it passes through a sieve having a pore size of 0.45 mm (BSS 36 or ASTM 40).

A 5 gm powdered sample is mixed in 50 ml of distilled water by stirring for pH measurement by a pH meter. Normal pH of fresh refuse is around 7. On decomposing, it tends to become acidic and a stabilized refuse has normally alkaline pH.

A 10 gm portion of the dried ground sample is placed in a silica dish and slowly heated in an electric furnace to $700^0C$ for 30 min. The residue is weighed and the loss of weight is indicated as organic matter and expressed as percent by weight. The organic content of refuse indicates the amount of compost that could be produced from it.

The carbon percentage is found out by using New Zealand formula in which the percent organic matter is divided by 1.724. Total nitrogen is obtained by the Kjeldahl method and the phosphorous and potassium estimated by using the phosphomolybdic and flame photometric method. Nitrogen, phosphorous and potash values are important for composting.

5. Biological Analysis

Refuse as it is produced does not normally contain human intestinal parasites. In India and other developing countries, it is common to find refuse lying at such points where it is liable to come in contact with material containing parasites. In cities, which do not have a sewerage system, night- soil is often deposited along with refuse which transmits parasites.

The sample collected for biological analysis is immediately transferred to a plastic bag and sealed. In the laboratory, the material is thoroughly mixed with the moisture of the bag and a suspension prepared by using the modified formol ether technique. The suspension is taken in a Sedgewick rafter counting cell and subjected to microscopic observation for various human intestinal parasites.

The samples collected from 33 Indian cities indicated A. lumbricoides and T. trichiura to be the dominant parasites.