Anaerobic digestion is a commercial reality for several kinds of waste. Nonetheless, anaerobic digestion of single substrates presents some drawbacks linked to substrate characteristics. Anaerobic co-digestion, the simultaneous digestion of two or more substrates, is a feasible option to overcome the drawbacks of mono-digestion and to improve plants economic feasibility. At present, since 50% of the publication has been published in the last two years, anaerobic co-digestion can be considered the most relevant topic within anaerobic digestion research. The aim of this paper is to present a review of the achievements and perspectives of anaerobic co-digestion within the period 2010-2013, which represents a continuation of the previous review made by the authors [3]. In the present review, the publications have been classified as for the main substrate, i.e., animal manures, sewage sludge and biowaste. Animal manures stand as the most reported substrate, agro-industrial waste and the organic fraction of the municipal solid waste being the most reported co-substrate. Special emphasis has been made to the effect of the co-digestion over digestate quality, since land application seems to be the best option for digestate recycling. Traditionally, anaerobic co-digestion between sewage sludge and the organic fraction of the municipal solid waste has been the most reported co-digestion mixture. However, between 2010 and 2013 the publications dealing with fats, oils and greases and algae as sludge co-substrate have increased. This is because both co-substrates can be obtained at the same wastewater treatment plant. In contrast, biowaste as a main substrate has not been as studied as manures or sewage sludge. Finally, three interdisciplinary sections have been written for addressing novelty aspects in anaerobic co-digestion, i.e., pre-treatments, microbial dynamics and modeling. However, much effort needs to be done in these later aspects to better understand and predict anaerobic co-digestion.

A critical review on anaerobic co-digestion achievements between 2010 and 2013

Increased biogas production at wastewater treatment plants through co-digestion of sewage sludge with grease trap sludge from a meat processing plant.

Municipal solid waste (MSW) management is becoming a serious issue in all over the world. Anaerobic digestion (AD) is one of the technologies to convert that waste into useful form of energy. But megacities like Singapore having limited resources, cannot fulfill the cow dung or other animal manure requirements in AD. Therefore there is a need to study critically the operating parameters and also the pretreatment technologies available for treating the substrate so that one can get the maximum output with limited input. To fulfill the need, the present paper deals with the review of various operating parameters and their effects on AD. This paper also reviews different pretreatment methods including mechanical, thermal, chemical and biological methods to improve the effectiveness of AD of MSW.

A comprehensive review on operating parameters and different pretreatment methodologies for anaerobic digestion of municipal solid waste

Anaerobic co-digestion of fat, oil, and grease (FOG): a review of gas production and process limitations.

High-solids anaerobic co-digestion of sewage sludge and food waste in comparison with mono digestions: Stability and performance

Co-digestion of grease trap sludge and sewage sludge.

Wave damping in vegetation in shallow lakes reduces resuspension and thereby improves the light climate and decreases nutrient recycling. In this study, wave transformation in reed (Phragmites australis) was measured in a shallow lake. Theoretical models of wave height decay, based on linear wave theory, and transformation of the probability density function (PDF), using a wave-by-wave approach, were developed and compared to the collected data. Field data showed an average decrease in wave height of 4–5% m/sup -1sup/ within the first 5–14 m of the vegetation. Incident root-mean-square wave height was 1–8 cm. A species-specific drag coefficient CD was found to be about 9 (most probable range: 3–25). CD showed little correlation with a Reynolds number or a Keulegan-Carpenter number. The PDF for the wave heights did not change significantly, but for longer distances into the vegetation and higher waves it tended to be more similar to the developed transformed distribution than to a Rayleigh distribution. Relationships developed in this study can be employed for management purposes to reduce resuspension and erosion. (Less)

http://lup.lub.lu.se/search/ws/files/4282872/1600043.pdf

Wave Damping in Reed: Field Measurements and Mathematical Modeling

Sediment resuspension can significantly affect the light climate and internal nutrient loading in shallow lakes. To predict wind-induced resuspension, a critical bottom shear stress or critical depth for the whole lake is typically used. It is suggested here that the availability of resuspendable material must also be considered and that this availability depends on local wind characteristics. The objective of this study was to show a connection between patterns of resuspension and accumulation of sediments and the prevailing wind directions. The near-shore sediments in the shallow Lake Krankesjon (surface area = 3 km2) in southern Sweden were characterized by a 5-graded resuspension potential scale and organic content. The spatial variability in sediment characteristics was compared to local wind statistics. This comparison showed that bottoms with low resuspension potential (sandy with low organic content) were located where waves from prevailing wind direction were acting, and bottoms with high resuspension potential (soft sediments with high organic content) were located to the lee-side of the prevailing wind directions. Intensive continuous turbidity measurements showed that winds above 10 m/s in directions other than the prevailing ones brought much material in suspension, while winds in the prevailing direction did not cause any increase in turbidity. The prevailing winds erode the bottom on one side of the lake, depositing resuspended material predominantly on the opposite side, where it can be resuspended by winds from non-revailing directions. Information about the local wind pattern can improve modeling and understanding of resuspension and redistribution of ediments in shallow lakes.

The role of non-prevailing wind direction on resuspension and redistribution of sediments in a shallow lake

Differential heating of surface waters of lakes caused by shading from vegetation can induce convection, which could be significant for the ecosystem because the chemistry and biology can differ in the reed belt zone compared to the open lake. This process has been given little attention in the literature. In the present study surface currents just outside a reed belt as well as radiation and water temperature profiles within and outside the vegetated belt were measured in a shallow lake in southern Sweden to determine the lateral flux between the two zones. The measured surface current directed toward the vegetation was about 1 cm/s. Net radiation at the water surface was 85% lower within the vegetation than in the open lake. The water surface temperature during sunny days was on average 0.5 degrees C warmer outside the reed belt, and at maximum 1 degrees C warmer. The lateral heat flux from the open water into the water within the reeds was estimated to similar to 200 W/m(2) during midday on sunny days, which corresponded to a calculated maximum current of 1.5 cm/s. This current between the open water and the reed vegetation is presumably the main water exchange process between the two zones during sunny summer days with low wind speeds. (Less)

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008WR006949

Charlotta Borell Lövstedt

Papers

Co-digestion of grease trap sludge and sewage sludge.

Wave Damping in Reed: Field Measurements and Mathematical Modeling

The role of non-prevailing wind direction on resuspension and redistribution of sediments in a shallow lake

Density-driven current between reed belts and open water in a shallow lake

Seasonal variation in resuspension in a shallow Swedish lake - Potential factors