Municipal wastewater sludge has become an issue of concern in Lebanon with the expansion of the numerous municipal wastewater treatment plants that have been put into operation. As an initial provision, the sludge was assumed to be sent to landfills for final disposal. However, the high amount of daily sludge generated, have imposed a serious threat on the lifespan of landfills thus preventing municipal solid waste landfills from receiving them. Additionally, the local standards for sludge management are either absent or non-comprehensive.
Some Common International Sludge Management Approaches
Internationally, there has been several practices. These practices have included landfilling, use in agriculture, and incinerating. Landfilling has been a common practice; however, due to the texture and nature of the sludge, it may require mixing it with other material to enable processing at landfills. Use for agricultural purposes, has been an issue of debate over recent years, especially, that the sludge in general is rich in nutrients such as phosphorous; however, various countries are moving towards banning such practices (i.e. Germany in 2018). The main reason behind this motion towards banning sludge in agricultural usage despite having it comprising of various nutrients that make it suitable for agricultural use, are that it may comprise as well traces of hormones and medications, thus imposing a concern on exposing humans to low percentage of such medications upon usage. Incineration of sludge has become a common practice in many developed countries especially after drying it. Many of the incineration techniques have been accompanied with systems to extract useful nutrients (such as phosphorous) from the sludge before incinerating it.
Lebanon with Respect to International Sludge Management Approaches
Landfilling of sludge is usually a low liability approach. Usually, it requires drying then disposing the sludge in landfills. However, the texture of sludge which is closer to a clayish nature may impose a limitation on using it alone in a landfill dedicated for sludge. Thus, it may need to be mixed with other material for landfilling. However, due to the limited area of Lebanon, and to the horizontal spread out of residences, allocating a suitable site for landfilling may be challenging. One may consider old quarry sites as an option, where the utilization of the sludge will contribute on the long run to quarry rehabilitation.
When it comes to using the sludge for agricultural practices, there are two concerns for the case of Lebanon. The first concern is mainly related to the connection of industrial areas to the municipal wastewater network and thus there will always be a risk at any time a failure happens in the industrial area, to end up with contaminated sludge, not to forget the risk of obtaining traces of medications in the sludge. The second concern is the lack of national norms and standards for such applications. Internationally, each country has almost its own customized legislations for such applications and accordingly, Lebanon will have to develop such norms and standards based on the type of plantations and type of available soil, in addition to acceptable parameters of various elements within the sludge.
As for incineration of sludge, well incineration in general has been a controversial topic in Lebanon as it is the case in many other countries. Incineration of sludge would require stringent regulations when it comes to operation and management of the incinerator and its emissions and residues. Furthermore, a controversy may remain when it comes to management and disposal of ash specifically the fly ash, since there are no suitable infrastructure available.
As a first step and to ensure the sustainability of any approach, a cost recovery system for sludge management must be established. Thereafter, it might be best to run several approaches in parallel, in order to capitalize on time. On the short-term, measures will be oriented towards using the sludge after drying it in rehabilitation of an existing quarry site. The rehabilitation may include adding other material in addition to the sludge depending on the nature and requirement of the site. In parallel legislations to govern agricultural usage and incineration should be developed. Such legislations may either ban such practices or impose clear standards and norms for such practices. Once the legislations are developed and put into force, the sludge infrastructure may be developed in line with these legislations.