当前世界环境

Introduction

Uncontrolled growth of the urban population in developing countries in recent years has made solid waste management an important issue¹．urbanizati率on has improved quality of life but at same time it has adverse effect on environment. Urbanization is increasing the level of air, noise, water pollution and solid waste generation their complexities²．几十年前,环境没有任何concern of scientific efforts for developing countries like India and even solid waste management was not prime concern in developing countries. The quantity of MSW has increased tremendously with improved life style and social status of the populations in urban centers³．Waste management and disposal is a big issue that India is facing today, since about 90% of waste is currently disposed of by open dumping⁴．The generation of solid waste causes air, water and odour pollution. The municipal solid waste management is not well structured at many places in India⁵．Municipal corporations in developing countries are not able to handle increasing quantities of waste, which results in uncollected waste on roads and in other public places⁶．固体废物管理中是一个至关重要的rvices provided by municipal authorities in the country to keep urban centers clean. It has been noticed that 90% of municipal solid waste (MSW) is dumped in open area which creates problem to public health and the environment⁷．The mixed municipal solid waste are dumped at the site and left to self-degradation and management⁸．Looking at the situation of MSW, some non-governmental organizations initiated working in the direction to highlight the pathetic situation of MSW of Indian cities. The activities of the public and various organizations resulted in the importance of MSW aspects of environmental management. Municipal solid waste (MSW) is an essential by-product of everyday living⁹．The proper segregation at the site, collection from the site, transportation and disposal to landfills site could be effective to manage MSW[10]. Geographical Information System (GIS) based approach is used for selecting optimum routing option for transportation of MSW¹．The important role also can be seen of Zero waste technology using reuse and recycling the waste.

The study is carried for solid waste management in Patna city. It generates 511 Ton/day solid waste where 51.96% compostable, 12.57% recyclable, 36% moisture and 0.37 kg/c/day waste generation rate with 18.62 C/N ratios¹¹．Municipal Solid Waste (MSW) in Patna is disposed of in an unscientific manner without considering environmental impacts²．The amount of recovered methane gas is estimated here.

Study Area

Patna city is situated at Southern Bank of Ganga with ‘B’ category of town. The city is approximately 35 km long and 16 km wide and divided into seventy two wards. This is the capital of Bihar state of India whose population is 13.7 lakh as per 2001 Census and area is 107 km²．Studies are done for the solid waste problem in six areas of Patna with reference to the total generation of solid waste/day/household, quality of the solid waste, awareness level and performance of Patna Municipal Corporation (PMC).

Figure 1: Study area “Patna” Click here to View figure

Methodology

A reviewfor municipal solid waste management of India reported physical characteristics of municipal solid waste for many metrocities¹²．So, the physical characteristics of solid waste for Patna city were taken from^12.The typical percentage of moisture content, density and energy content for each component were used to calculate the same for MSW in this study (Ali et al., 1999). Chemical composition was estimated for MSW using typical values of MSW component¹³．Chemical characterization was done for carbon, hydrogen, oxygen, nitrogen and sulfur for each component of MSW then the same was calculated for MSW. Afterwards, mass was calculated for chemical composition and chemical formulation was made using molar weight.

Results and Discussion

Moisture content (%), dry mass (kg), volume and total energy for MSW have been calculatedin Table 1. The overall moisture content and density for MSW is35.43% and 204 kg/m³．The energy content as discarded solid waste is 8.4 MJ/kg while energy content for dry ash and ash free dry ash are 13 and 14.1 MJ/kg. Here, 5% ash content was assumed.

The total MSW generation in Patna city is 511 tons/day and the total dry mass of MSW is 330 tons/day. The total energy content (Dry Ash) is 4.3×10⁶MJ/day while energy content (Ash free Dry Ash) is 4.4×10⁶MJ/day. The chemical composition of MSW has been shown in Table 2 and Table 3.

表1:物理特性的固体废物or Patna city (By weight)

Name of Component	% of Composition	Moisture Content %	Dry Mass (kg)	Density (kg/m3)	Volume (m3)	Energy (MJ/kg)	Total Energy (MJ)
Paper	4	6	3.76	85	0.047	16.75	67
Textile	5	10	4.5	65	0.078	17..45	87.25
Leather	2	10	9.8	160	0.031	17.45	34.9
Plastic	6	2	5.88	65	0.092	32.60	195.6
Metal	1	3	0.97	320	0.003	0.70	0.7
Glass	2	2	1.96	198	0.010	0.15	0.3
Ash, fine other	35	8	32.2	480	0.073	7	245
Compostable	45	70	13.5	290	0.155	4.65	209.25
Total	100		64.57		0.49		840

The oxygen requirement for MWS is 1.9×10⁵kg O₂/day or 1.33×10⁸L of O₂/day to degrade MSW. The present MSW of Patna city can generate methane gas (CH₄) 2.46×10⁵kg/day 3.44×10⁸L/day and carbon dioxide (CO₂) 5×10⁵kg/day or 2.55×10⁸L/day. The recovery from solid waste can be utilized to proper landfilling of MSW.

Table 2: Chemical Characteristics of Solid Waste

Component	Wet mass (Kg)	Dry mass (kg)	C	H	O	N	S	Ash
Paper	4	3.76	1.64	0.864	5.076	0.351	0.054	0.675
Textile	5	4.5	2.475	0.23	1.65	0.0112	0.007	0.23
Leather	2	9.8	1.08	0.03	1.404	0.207	0.007	0.112
Plastic	6	5.88	3.53	0.144	0.208	0.18	0.007	0.18
Metal	1	0.97	-	0.42	1.34	-	-	0.59
Glass	2	1.96	-	-	-	-	-	-
Ash, fine other	35	32.2	8.47	-	-	-	-	-
Compostable	45	13.5	6.48	0.97	0.64	0.161	0.06	21.896
Total	100	64.57	23.68	2.76	10.32	0.910	0.13	23.68

Table 3: Ultimate Analysis of Combustible Components

Component	Mass (kg)	Kg/mole	Mole	Ratio w.r.t. S	Ratio w.r.t. N
C	23.68	12	1.97	492.5	28.14
H	2.67	1	2.67	667.5	38.14
O	10.32	16	0.645	161.25	9.14
N	0.91	14	0.07	17.5	1
S	0.41	32	0.004	1

Chemical Formula MSWis given below in equation (1) and (2).

C_492.5H_667.5O_161.25N_17.5S ...(1)
C_28.14H_38.14O_9.14N_17.5．..(2)

Molecular weight = 536.06 kg

Oxygen required for complete aerobic stabilization

Since 536.06 kg solid waste requires 32.35×32 kg O₂

Recovery of Methane Gas

Recovery of Carbon Dioxide Gas

Conclusions

In India and many other developing countries, the segregation, collection, transportation and disposal of municipal solid waste (MSW) are generally done in a very unscientific way presently. This leads problems for environment in terms of water, air and odour pollution. This paper presented a study for solid waste management for an urban city Patna of India. The components of MSW have been estimated and based on that, 35.43% moisture, 204 kg/m³density and 14.1 MJ/kg (dry ash) energy content have been quantified. Afterwards, chemical compositions have been calculated and chemical formula has been made as C_28.14H_38.14O_9.14N_17.5for MSW. This composition can help to estimate 1.33×10⁸L of O₂/day requirement of oxygen to degrade MSW and recovery of 3.44×10⁸L of methane/day and 2.55×10⁸L of carbon dioxide/day from MSW.

Generally, landfill for solid waste management is planned for fifteen years or more than that. It is carried out in several parts or layers which take many years. The calculation of energy content, requirement of oxygen to degrade MSW and recovery of methane, carbon dioxide from MSW have been carried out for a year which can be extended for whole landfill period.

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