Sources of Wastes

Process wastes arise from a variety of sources which are associated with the chemistry and plant. They may arise from the preparation of feedstocks the reaction/reactor itself from product separation and from the utility system, particularly combustion emissions associated with provision of heat and electrical power [13]. Plant operations also contribute and smart operation of a process which is certainly not inherently clean can sometimes do a good deal to minimise the production of wastes. This book is, however, concerned with the chemistry of waste minimisation, rather than chemical engineering and operations, both of which are of great importance. 

There are several ways in which the chemistry of a process can cause a waste problem. Reactions which cause particular difficulties are those which give stoichiometric amounts of waste  

---

Feed purification. Impurities that enter with the feed inevitably cause waste. If feed impurities undergo reaction, then this causes waste from the reactor, as already discussed. If the feed impurity does not undergo reaction, then it can be separated out from the process in a number of ways, as discussed in Sec. 4.1. The greatest source of waste occurs when we choose to use a purge. Impurity builds up in the recycle, and we would like it to build up to a high concentration to minimize waste of feed materials and product in the purge. However, two factors limit the extent to which the feed impurity can be allowed to build up ... 

Sources of waste in process operations a. Start-up I shutdown in continuous processes... 

There are many other sources of waste associated with process operations which can only be taken care of in the later stages of design or after the plant has been built and has become operational. For example, poor operating practice can mean that the process operates under conditions for which it was not designed, leading to waste. Such problems might be solved by an increased level of automation or better management of the process. These considerations are outside the scope of this text. 

Utility systems as sources of waste. The principal sources of utility waste are associated with hot utilities (including cogeneration systems) and cold utilities. Furnaces, steam boilers, gas turbines, and diesel engines all produce waste from products of combustion. The principal problem here is the emission of carbon dioxide, oxides of sulfur and nitrogen, and particulates (metal oxides, unbumt... 

These sources of waste from the steam system can be reduced by increasing the percentage of condensate returned (in addition to reducing steam generation by increased heat recovery). 

As in all the processes, the process condensate and all other sources of waste urea—NH —water contamination go to a waste recovery unit which includes a urea hydrolyzer. The final water discharge is then below 3—5 ppm of NH and urea. 

Water as coolant in a nuclear reactor is rendered radioactive by neutron irradiation of corrosion products of materials used in reactor constmction. Key nucHdes and the half-Hves in addition to cobalt-60 are nickel-63 [13981 -37-8] (100 yr), niobium-94 [14681-63-1] (2.4 x 10 yr), and nickel-59 [14336-70-0] (7.6 x lO" yr). Occasionally small leaks in fuel rods allow fission products to enter the cooling water. Cleanup of the water results in LLW. Another source of waste is the residue from appHcations of radionucHdes in medical diagnosis, treatment, research, and industry. Many of these radionucHdes are produced in nuclear reactors, especially in Canada. 

Document all types, quantities, and sources of wastes (both nonbazardoiis and hazardous wastes). 

A systematic program should he undertaken to examine all sources of waste production and to develop alternative operations and processes to reduce waste generation. 

You should use the material balance information to identify the major sources of waste and pollution, to look for deviations from the norm in waste production, to identify areas of unexplained losses, and to pinpoint operations that contribute to flows that exceed national-, local-, or site-discharge regulations. Also, a good thing to remember is that, from a practical standpoint, process ciency is synonymous with waste minimization. 

The process has two main sources of waste water. These are the condensate streams from the steam strippers. The principal pollutant in both wastewater streams is phenol. Phenol is of concern primarily because of its toxicity, oxygen depletion, and turbidity. In addition, phenol can cause objectionable taste and odor in fish flesh and potable water. 

Besides scrap and worn tires, other main sources of waste mbber are discarded mbber products, such as mbber pipes, mbber belts, mbber shoes, edge scraps, automobile hoses, and various fabric-reinforced components. Scraps produced during the production of mbber goods also contribute to recycle stream [6]. Reutilization of waste mbber demanded effective techniques for its recycling. 

As mentioned several times Lewis acids are highly valuable catalysts but the most commonly used ones such as aluminium chloride and boron trifluoride are highly water sensitive and are not usually recovered at the end of a reaction, leading to a significant source of waste. In recent years there has been much research interest in lanthanide triflates (trifluoro-methanesulfonates) as water stable, recyclable Lewis acid catalysts. This unusual water stability opens up the possibility for either carrying out reactions in water or using water to extract and recover the catalyst from the reaction medium. 

Environmental aspects are very important in the development of a process concept. The formation of pollutants (everything that is not product is waste) should be prevented and efficient strategies for treatment of effluents should be developed. Sources of wastes are... 

Sources of wastes must be identified and reduced as much as possible. In addition, processing of unavoidable wastes must be incorporated in the design (see Section 5.2.5). 

Waste Generated Source of Waste Method Generated (Ib/yr) Management Cost... 

The BDS system is capable of processing brine with much higher sulphate concentrations. In one case, a source of waste brine bearing high sulphates was available at no cost. The only problem was finding an economical way to lower the sulphate level. Since the brine was free, maximisation of NaCl recovery efficiency was not a priority. As discussed above, operating conditions of the process may be varied to optimise capital cost, brine recovery efficiency or purity levels, as required. Typical data at higher sulphate levels are shown in Table 24.2. 

Biomass energy created by waste and residues left after food processing operations, and landfill gas mainly produced during anerobic decomposition of organic waste material seem to offer the most promising source of waste heat engines. The material is already concentrated at the processing site and it creates a disposal pollution problem. 

The major discharges from sulfuric acid alkylation are the spent caustics from the neutralization of hydrocarbon streams leaving the alkylation reactor. These wastewaters contain dissolved and suspended solids, sulfides, oils, and other contaminants. Water drawn off from the overhead accumulators contains varying amounts of oil, sulfides, and other contaminants, but is not a major source of waste. Most refineries process the waste sulfuric acid stream from the reactor to recover clean acids, use it to neutralize other waste streams, or sell it. 

These are relatively clean processes because care is taken to avoid loss of product through spillage. The primary source of waste material is from the washing of railroad tank cars or tankers prior to loading finished products. These wash waters are high in emulsified oil. 

The idea of the continuous improvement is to reduce or eliminate activities that do not add value and thus are wasteful. In fact, there are many activities in any laboratory that need to be reconsidered. Below are summarized the seven sources of waste that any organization should avoid. 

---