Treatment of municipal wastewater results worldwide in the production of large amounts of sewage sludge. The major part of the dry matter content of this sludge consists of nontoxic organic compounds, in general a combination of primary sludge and secondary (microbiological) sludge. The sludge also contains a substantial amount of inorganic material and a small amount of toxic components. There are many sludge-management options in which production of energy (heat, electricity, or biofuel) is one of the key treatment steps. The most important options are anaerobic digestion, co-digestion, incineration in combination with energy recovery, co-incineration in coal-fired power plants, co-incineration in combination with organic waste focused on energy recovery, use as an energy source in the production of cement or building materials, pyrolysis, gasification, supercritical (wet) oxidation, hydrolysis at high temperature, production of hydrogen, acetone, butanol, or ethanol, and direct generation of electrical energy by means of specific micro-organisms. Incineration and co-incineration with energy recovery and use of sewage sludge in the production of Portland cement are applied on a large scale. In these processes, the toxic organics are destructed and the heavy metals are immobilized in the ash or cement. The energy efficiency of these processes strongly depends upon the dewatering and drying step. It is expected that these applications will strongly increase in the future. Supercritical wet oxidation is a promising innovative technology but is still in the development stage. With the exception of biogas production, the other biological methods to produce energy are still in the initial research phase. Production of biogas from sewage sludge is already applied worldwide on small, medium, and large scales. With this process, a substantial experience exists and it is expected that this application is getting more and more attention. Besides the increasing focus on the recovery and reuse of energy, inorganics, and phosphorous, there is also an increasing focus to solve completely the problem of the toxic organics and inorganic compounds in sludge. In the assessment and selection of options for energy recovery by means of biological methods, this aspect has to be taken into account.

The presence of the synthetic nonionic surfactants Triton X-100, Tergitol NPX, Brij 35, and Igepal CA-720 resulted not only in increased apparent solubilities but also in increased maximal rates of dissolution of crystalline naphthalene and phenanthrene. A model based on the assumption that surfactant micelles are formed and act as a separate phase underestimated the dissolution rates; this led to the conclusion that surfactants present at concentrations higher than the critical micelle concentration affect the dissolution process. This conclusion was confirmed by the results of batch growth experiments, which showed that the rates of biodegradation of naphthalene and phenanthrene in the dissolution-limited growth phase were increased by the addition of surfactant, indicating that the dissolution rates were higher than the rates in the absence of surfactant. In activity and growth experiments, no toxic effects of the surfactants at concentrations up to 10 g liter ؊1 were observed. Substrate present in the micellar phase was shown to be not readily available for degradation by the microorganisms. This finding has important consequences for the application of (bio)surfactants in biological soil remediation.

No abstract

No abstract

No abstract

No abstract

Persulfate oxidation was validated as a method to predict polycyclic aromatic hydrocarbon (PAH) bioavailability in soils and sediments. It was demonstrated for 14 field contaminated soils and sediments that residual PAH concentrations after a short (3 h) persulfate oxidation correspond well to residual PAH concentrations after 21 days of biodegradation. Persulfate oxidation of samples that had first been subjected to biodegradation yielded only limited additional PAH oxidation. This implies that oxidation and biodegradation removed approximately the same PAH fraction. Persulfate oxidation thus provides a good and rapid method for the prediction of PAH bioavailability. Thermogravimetric analysis of oxidized and untreated samples showed that persulfate oxidation primarily affected expanded organic matter. The results indicate that this expanded organic matter contained mainly readily bioavailable PAHs.

The crude palm oil industry plays an important role in the economic development of Thailand and in enhancing the economic welfare of the population. Despite obvious benefits of this industrial development, it also significantly contributes to environmental degradation, both at the input and the output sides of its activities. On the input side, crude palm oil mills use large quantities of water and energy in the production process. On the output side, manufacturing processes generate large quantities of wastewater, solid waste/by-products and air pollution. Current industrial wastes and recoverable materials are empty fruit bunches, fibers, shells and ash. It is estimated that in 2003, a total of 2.1 million ton of solid wastes/by-products and 2.5 million m 3 of wastewater were generated. The concept of the industrial ecosystem points at the potential of industrial waste recycling resembling food chains, food webs and nutrient cycles of nature. Following the notion of industrial ecology crude palm oil mills can develop a number of waste recycling and reuse systems. This paper analyzes the nature of these industrial ecosystems, divided in in-plant ecosystems (clean technology options) and external waste exchange between crude palm oil industries and other economic activities in Thailand.