Impact of temperature and residence time on sewage sludge pyrolysis for combined carbon sequestration and energy production.

Environmental challenges related to sewage sludge call for urgent sustainable management of this resource. Sludge pyrolysis might be considered as a sustainable technology and is anticipated to support measures for mitigating climate change through carbon sequestration. The end products of the process have various applications, including the agricultural utilization of biochar, as well as the energy exploitation of bio-oil and syngas. In this research, sewage sludge was pyrolyzed at 500 °C, 600 °C, 750 °C, and 850 °C. At each temperature, pyrolysis was explored at 1hr, 2hrs, and 3hrs residence times. The ratio (H/Corg)at was tapped to imply organic carbon stability and carbon sequestration potential. Optimum operating conditions were achieved at 750 °C and 2hrs residence time. Produced biochar had (H/Corg)at ratio of 0.54, while nutrients' contents based on dry weight were 3.99%, 3.2%, and 0.6% for total nitrogen (TN), total phosphorus (TP), and total potassium (TK), respectively. Electrical conductivity of biochar was lesser than the feed sludge. Heavy metals in biochar aligned with the recommended values of the International Biochar Initiative. Heat content of condensable and non-condensable volatiles was sufficient to maintain the temperature of the furnace provided that PYREG process is considered. However, additional energy source is demanded for sludge drying.

Effect of increasing the surface area of primary sludge on anaerobic digestion at low temperature.

Two sets of reactors were operated at 15°C and at sludge retention times (SRTs) of 65 days and 30 days, respectively. Each set was operated at six different mixing velocities. Shear forces provided by mixing affected particle size distribution and resulted in different sludge surface areas. The aim was to investigate the effect of increasing primary sludge surface area on anaerobic digestion at low temperature. The maximum surface areas at the applied mixing velocities were 5926 cm2/cm3of sludge and 4672 cm2/cm3 of sludge at SRTs of 65 days and 30 days, respectively. The corresponding calculated methanogenesis were 49% and 15% at SRTs of 65 days and 30 days, respectively. Maximum total solids (TS) reductions were 26% and 11% at 65 days and 30 days SRTs, respectively. Lipase activity increased with increasing SRT and sludge surface area. Results clearly showed that increasing sludge surface area improved sludge digestion at 15°C.

Anaerobic treatment of strong sewage by a two stage system of AF and UASB reactors.

An anaerobic treatment system that consists of an Anaerobic Filter (AF) and an Upflow Anaerobic Sludge Blanket (UASB) in series was built and operated to investigate its performance in treating strong domestic wastewater with high suspended solids fraction under Jordan's ambient temperatures of 25 degrees C for summer and 18 degrees C for winter. The system was operated from September 2003 until early April 2004. The system was operated at a Hydraulic Retention Time (HRT) of 4 hours for the first stage AF and 8 hours for the second stage UASB. Average COD(t) and COD(ss) removal efficiencies of the AF/UASB were 58% and 81% respectively for the operation period. The results showed that the first stage AF was effective in removing suspended solids. In addition, hydrolysis, acidification and methanogenesis took place in the first stage AF which was advantageous to the second stage UASB. It was concluded that the AF/UASB system is effective in treating strong domestic wastewater with high suspended solids content under Jordan's ambient temperatures.

Sequential anaerobic-aerobic treatment for domestic wastewater - a review.

Introduction, consolidation and even standardization of expensive conventional aerobic systems for domestic wastewater treatment imposed significant financial constraints on the expansion of sanitary services including treatment in developing countries. A viable alternative is the sequential anaerobic-aerobic systems. If compared with the conventional aerobic technologies based on activated sludge processes, lower energy consumption and lower excess sludge production can be achieved with a high-rate anaerobic pre-treatment step. Particularly with concentrated sewage, the energy benefit of applying anaerobic pre-treatment will become very significant. This study aims on putting the effectiveness of sequential systems for treatment of domestic wastewater on view, through displaying results presented in literature on the performance of these systems.

Conservation of ammonia during food waste composting.

An experiment was conducted to quantify ammonia (NH3) losses during food waste composting and to evaluate the effectiveness of mature aerobic sewage sludge/olive pomace compost and phillipsite/chabazite zeolite in reducing NH3 losses during composting. Food waste amended with chopped barley straw was composted for a period of 68 days in three in-vessel reactors. The mature aerobic sewage sludge/olive pomace compost and the zeolite were placed on a mesh tray above the waste mixture in the first and second reactors, respectively. The third reactor contained straw-amended food waste only and served as a control. It was found that the mature aerobic sewage sludge/olive pomace compost reduced NH3-N losses by 36% of initial TN through nitrifying volatilized NH3 into nitrate (NO3-). Zeolite reduced NH3-N losses by 41% of initial total nitrogen due to adsorption of volatilized NH3. The use of mature compost in conservation of nitrogen is a promising cheap method; however, it needs further optimization and research.

Grey water characteristics and treatment options for rural areas in Jordan.

Low water consumption in rural areas in Jordan had resulted in the production of concentrated grey water. Average COD, BOD and TSS values were 2568mg/l, 1056mg/l and 845mg/l, respectively. The average grey water generation was measured to be 14L/c.d. Three different treatment options were selected based on certain criterions, and discussed in this article. The examined treatment systems are septic tank followed by intermittent sand filter; septic tank followed by wetlands; and UASB-hybrid reactor. Advantages and disadvantages of each system are presented. It was concluded that UASB-hybrid reactor would be the most suitable treatment option in terms of compactness and simplicity in operation. The volume of UASB-hybrid reactor was calculated to be 0.268m(3) with a surface area of 0.138m(2) for each house having 10 inhabitants on average. Produced effluent is expected to meet Jordanian standards set for reclaimed water reuse in irrigating fruit trees.

Effect of SRT and temperature on biological conversions and the related scum-forming potential.

Sludge flotation was reported to cause several operational problems in anaerobic systems including UASB reactors treating both strong domestic sewage and some industrial wastewater. This research is to investigate the effect of anaerobic digestion on scum-forming potential (SFP) of sludge and other physical-chemical properties. A simple test was developed to measure and compare the tendency of different sludge to form a scum layer. Results showed that anaerobic digestion affects chemical composition of sludge flocs and consequently, SFP, which was found to be inversely proportional to the degree of digestion (both SRT and temperature). It was suggested that higher protein concentration at elevated SRT and 25 degrees C increased the negative surface charge of sludge flocs and ,consequently, reduced the ability of sludge to attach to gas bubbles and float. Floc average size increased with increasing SRT and temperature, especially for sludge with 75d SRT at 25 degrees C. On the other hand, settling properties of sludge were negatively affected by increasing SRT to 75d at 25 degrees C. Filterability had a strong positive correlation with average floc size, but also polymeric constituents correlated positively with filterability at 25 degrees C.

Treatment of strong domestic sewage in a 96 m3 UASB reactor operated at ambient temperatures: two-stage versus single-stage reactor.

A 96 m3 UASB reactor was operated for 2.5 years under different conditions to assess the feasibility of treating strong sewage (COD(tot) = 1531 mg/l) at ambient temperatures with averages of 18 and 25 degrees C for winter and summer respectively. During the first year, the reactor was operated as a two-stage system at OLRs in the range of 3.6-5.0 kg COD/m3 d for the first stage and 2.9-4.6 kg COD/m3 d for the second stage. The results of the first stage showed average removals of 51% and 60% for COD(tot) and COD(ss) respectively without significant effect of temperature. The second stage reactor was unstable. The temperature affected sludge stabilization. During the second year, the first stage was operated as a single-stage UASB reactor at half of the previous loading rates. The results showed an average removal efficiency of 62% for COD(tot) during summer, while it dropped to 51% during wintertime. However, the effluent suspended solids were stabilized with VSS/TSS ratio around 0.50 all over the year. The sludge in the single-stage reactor was well-stabilized and exerted an excellent settlability. During the last three months of research, sludge was discharged regularly from the single-stage UASB reactor. The results showed no significant improvement in the performance in terms of COD(tot). Based on the results of the experiment, a single-stage UASB reactor operated at relatively long HRT is preferred above two-stage system at the Jordanian conditions.

Short report: outbreak of cutaneous leishmaniasis in a nonimmune population of soldiers in Wadi Araba, Jordan.

An outbreak of zoonotic cutaneous leishmaniasis (ZCL) occurred in a battalion of 80 soldiers posted at Qurayqira camp in Wadi Araba in southern Jordan. The battalion spent an intermittent period of five and a half months in the area, during which 45.0% (36 of 80) of the soldiers showed clinical disease. Of the 44 clinically negative soldiers, 31 were tested with leishmanin and 11 (35.5%) were leishmanin positive. The number of lesions in infected soldiers ranged from one to 15 and were mostly on the face and extremities. This report shows the level of transmission of ZCL in Wadi Araba, which is presently undergoing economic expansion and development following the peace process of the Arab-Israeli conflict.