ODOUR REDUCTION

To quantify odour reduction by aerobic and anaerobic treatment of liquid manures. 

To evaluate odour reduction from livestock buildings by the use of biofilters. 

Different methods are in use for avoiding the generation of odourous gases in sewage treatment systems. One of the most effective means are new operational routines like sewer cleaning programs, and odour reduction equipment at treatment plants. 

The results from total odour strength measurements of different chemical scrubbers, show odour reduction efficiencies between 95 per cent and 98 per cent. ED50 of the cleaned air has been found to be between 50 and 100, and the air has been characterized as free from sewage odours, but it smells like chemicals . It seems as if a chemical sembber always gives this scrubber odour . 

Use of carbon filter odour reduction is quite common at municipal wastewater treatment plants. The odour compounds are not destroyed in the filter, but only retained until the... 

The principle of burning odour components to highly oxidized products with little or no odour, is very old. If the temperature and contact time of the gases in the combustion chamber are sufficient, combustion of odour from a sewage treatment plant, without doubt, is the best odour reduction method. Contact time up to 3 seconds and temperatures of about 850°C have been reported as sufficient. (4) (5)... 

The City of Oslo has the only treatment plant in Norway using combustion to reduce odour. The plant has digesters and therefore low fuel costs. The efficiencies measured show a very good odour reduction, up to 98-99 per cent. No wastewater odour was recognized in the cleaned air, only a faint burnt odour . 

Extensive work has been carried out in the US regarding the use of soil filters for odour reduction. (6) It was shown that the filter performance depended on filter loading, type of soil, soil moisture, temperature and concentration of odourous components. The US study also concluded that both chemical and biological processes were responsible for the odour reduction. 

Only limited information is available regarding the design and use of iron oxide filters for odour reduction, although Cormack et al. describe the filters in their work. (7)... 

On the other hand there is sometimes the risk that odour reduction increases the volatilization of ammonia. This can be the case with under cage diying of poultry manure or with anaerobic digestion of liquid manure. 

Figure 1. Odour reduction efficiency in iron oxide filter expressed as a function of the gas flow through the filter.

Separation as a method of manure handling and odours reduction in pig buildings Measurements of the olfactometric efficiency of various odour control devices in rendering plants... 

ODOUR REDUCTION EFFICIENCY OF DIFFERENT TYPES OF COVERINGS AND THF.IR VAT. HATTON ACCORDING TO THF. GUIDELINE VDI 3471... 

According to the strict rules, as confirmed before, 25 points only should be accepted with at least 60 %, and 40 points with at least 85% odour reduction efficiency. 

The odour reduction efficiency can be measured by using an olfactometer and additional equipment. A constant air stream is passing through a hood, adjusted to the slurry surface, crust or cover. One part of the exhausted odour loaded air is fed into the olfactometer. 

From nearly tight coverings and roofs only a very small flow rate of produced gases can be emitted. The emission by air exchanging is set to zero. Therefore the odour reduction efficiency of those coverings compared with an uncovered open manure surface is 95 to 100%. 40 points can be accepted, fig.4. 

Fig.4. Odour reduction efficiency of different types of coverings...

Floating tarpaulins don t keep close to the wall. An open gap is unavoidable. The odour reduction efficiency is mostly not more than 80%. Only 25 points can be accepted. 

The impermeable floating mat shows nearly the same efficiency as a permeable tarpaulin and is much better than all tested artificial floating crusts. Among these only the combination of straw and plastic foam pellets shows an odour reduction of more than 60%, and 25 points can be accepted. 

Floating crusts set up just of straw or plastic foam pellets and makeshift solutions cannot be accepted. Their odour reduction is mostly less 60%. 

The better the odour reduction efficiency of the covering the higher the investment. Regarding the utilization period the costs per cubic meter liquid manure (and with that also per fattening pig) are about -0,3 DM per m3 for a 25-point-covering and -0,5 DM per m3 for a 40-point-covering. 

In table 1 some results from this study (2) of odour reduction are presented. The thresholds are mean values expressed as log dilution factors. Standard deviations are calculated on the averages of doubled ED-50 values, each value based on the reports of six observers at a time. As can be seen, incorporation of the manure largely reduced the emission of odour from the field. This mainly concerns the injection techniques, which in some cases reduced the odour to the background level. Conventional tillage implements such as a plow or a disc harrow also reduced the odour emission considerably. 

SEPARATION AS A METHOD OF MANURE HANDLING AND ODOURS REDUCTION IN... 

The filter material should consist of peat mixed with heather in order to keep the air resistance low. If the peat filter is to give maximum odour reduction the peat must be moist. 

Fig. 1. Principle of bio filter for odour reduction in the ventilation air according to Zeisig, H.D. et al 1982.

The Swedish filter has not yet been evaluated with regard to odour reduction. The filter was completed during December 1984 and the exceptionally cold winter has delayed the evaluation. However, measurements of odour thresholds will be made during both winter and summer conditions. 

Odour was determined in accordance with Standard Methods (A.P.H.A. 80). Table II shows how almost total deodorization is obtained when aera tion treatment is practised. With the other types of treatment, too, there is a reduction in odour, most marked in the second period of tests (Jul.—Oct.), when temperatures are higher. In this period odour reduction is already considerable after 60 days. 

A measure of the total organic material present in slurries can be obtained by determining chemical oxygen demand (COD) or biological oxygen demand (BOD) (3) and the latter measure is used by Water Authorities in relation to the pollution of water courses where oxygen tension in the water is a prime concern. In studies to evaluate aerobic digestion as a means of odour reduction, the dissolved volatile fatty acids are a useful measure of the potential odour nuisance (2). 

Table 3 The effects of different methods for odour reduction...

If there is a need for odour reduction on an animal husbandry farm anaerobic digestion is one of the real possibilities. The investment and running costs of the methods, mentioned in table 3, are indicated in previous chapters. An economic calculation for the feasibility of an anaerobic digestion is open for discussion. For our purpose we must valuate the nett output of biogas. 

Table 1 showed that for a 500-pig unit the annual losses are about Dfl. 7.000,-. These losses are calculated (7) under optimal conditions. When odour reduction is the first goal, losses can be higher. Suppose that 50% of the produced biogas is not used. The extra losses are 5000 m3 a Dfl. 0,52=Dfl. 2.600,- higher. So total losses increase to Dfl. 9.600,-. Per pigplace are the costs for odour reduction nearly Dfl. 20,-. 

---