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Archives (2003)

Sewage sludge: From stink to the sweet smell of profit? by Ma. Lizbeth Baroña

April-June 2003 Volume 5 No. 2

The study yielded proof that the sludge, or mud from sewage water is a potential source of nutrients, which improves the fertility of the soil for sugarcane farming. Hence, the idea that it can be a suitable substitute for chemical fertilizer.

Source: www.ukrivers.net/sewage.jpg

Sewers? One hardly gets away from the smell of the liquid waste underneath, as its odor forces its way out and into our nostrils. But a study conducted by the Sugar Regulatory Administration (SRA) of the Luzon Agricultural Research and Extension Center (LAREC) in Floridablanca, Pampanga says sugarcane growers will soon find something good from the repulsive smell.

An alternative to expensive fertilizers?
Making up a large portion of the expenses in sugarcane farming is the cost of fertilizer. The soil needs to have enough nutrients for it to be productive, therefore, making fertilizer a necessity in the farm.

Scientists in LAREC believe an alternative to costly fertilizers is soon in place. After analyzing the chemical composition of sewage sludge, the scientist made notable findings: the sludge contains high amounts of nitrogen, iron, calcium, magnesium, phosphorous, and potassium, as well as small amounts of manganese, copper, sodium, and zinc. It also has neutral acidity (pH), and has a considerable amount of organic matter, having come from household wastes.

The sludge is the sediment formed at the bottom of sewage waters. Whether dewatered, meaning the sludge has been drained of its water content - or in liquid, muddy form, the sewage sludge's organic content improves both the nutrient structure and ability of the soil to hold water. The water in the liquid sludge also adds moisture to the soil- an extra help especially during dry seasons.

Sewage sludge and N fertilizer
The scientists tested the effectiveness of the Nitrogen (N) fertilizer, combined with different amounts of the sewage sludge. They experimented on three main plots. On the first plot, they put no N fertilizer but the subplots were treated with different amounts of sewage sludge. This amounts are 0 t/ha, 40 t/ha, 80 t/ha, and 120 t/ha. On the second plot, they put 90 kg/ha of N fertilizer with subplots holding the different amounts of sludge mentioned. The third plot held 180 kg/ha of N fertilizer, tested again with the same set of varying amounts of sewage sludge.

To make sure that they are putting in reasonable amounts of N fertilizer on the plots, the scientists used the recommended rate of N fertilizer from LAREC. As for the amount of sewage sludge used, the Manila Water Co., the source of liquid sewage sludge, has no recommended rate of application for agricultural crops, therefore, they used varying amounts of the sludge.

The Phil 8583 variety of sugarcane was planted at 40,000 canes per hectare. After adding in the different amounts of sewage sludge in the plots, the scientists also put in the required amount of urea for sugarcane planting.

They let the sugarcane grow for 10 months. After harvesting the 10-month old sugarcanes, soil samples were taken for analysis of pH, organic content, and presence of potassium and phosphorus and other heavy metals.

Measuring up
It turned out that the height of the plant was significantly influenced by the combination of sewage sludge and the N fertilizer. Likewise, tillering also improved in the increasing amount of the sewage sludge at the 3 plots with different amounts of N fertilizer. It was also noted that applying sewage sludge notably improved early growth parameters of sugarcane.

The number of stalks, including how long they grow, was improved by the amounts of sewage sludge at the required amount of N fertilizer. Increasing the amounts of both the sludge, and the N fertilizer also increased in sugarcane yield. The highest amount of sugarcane harvest was seen at the 180 kg/ha N fertilizer and 120 T/ha sludge combination. Natural sugar content, though, was not influenced by any of the combinations.

Heavy metals in the sewage sludge - at different amounts at ton/hectare - is significantly less than the limit given by the Department of Environment and Natural Resources (DENR) Administrative Order No. 29. The metal content of the sludge did not increase in the soil, and also did not contaminate the soil with toxic substances.

A slight improvement, though, on the acidity (pH), organic matter, and exchangeable potassium on the soil was observed after harvesting, the greater the amount of sewage sludge, the better the characteristics of the soil.

Although the coliform level of the soil after the application of the sludge was high, bacterial count was below the DENR standard limit, and the soil was negative of protozoans or helminthic parasites. Thus, the sewage sludge was not a health hazard.

From stink to sweet
The profitability promise of the sewage sludge comes in the form of reducing the fertilization cost by almost 50%. Sugarcane yield after applying 80T/ha of sludge, on a plot with already a 90 kg/ha of N fertilizer, was comparable to the yield after applying 180kg/ha of N fertilizer, with or without sewage sludge. The cut on the expenses the farmer had to shell out by using 180kg of N fertilizer compared to using half of the amount of N, with the aid of the less costly sewage sludge is notable.

In addition, the choice of using sewage sludge is appealing considering the improvements in the soil properties after using sewage sludge. It ultimately left the soil environment less wanting of inorganic fertilizer.

Another advantage of the use of sewage waters as sugarcane farming fertilizer would be that it will significantly reduce the cost of liquid waste disposal.

Next time your nostrils tingle with that smell from underground, try not to be too repulsed for all you know, your frozen delight could be another product of the promise it brought.

Source: Productivity improvement of soils planted to sugarcane with liquid sewage sludge by Estanislao, EB; Manlapaz BG; Quilloy OT. Sugar Regulatory Administration, Luzon Agricultural Research and Extension Center, Floridablanca, Pampanga. Contact through: 045-970-0872 fax 045 970-0412, and email at sralarec@mozcom.com.

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